docs: filesystems: convert sharedsubtree.txt to ReST
- Add a SPDX header; - Adjust document and section titles; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add table markups; - Add it to filesystems/index.rst Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/6692b8abc177130e9e53aace94117a2ad076cab5.1588021877.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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@ -33,6 +33,7 @@ algorithms work.
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mount_api
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quota
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seq_file
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sharedsubtree
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automount-support
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@ -1870,7 +1870,7 @@ unbindable mount is unbindable
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For more information on mount propagation see:
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Documentation/filesystems/sharedsubtree.txt
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Documentation/filesystems/sharedsubtree.rst
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3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
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@ -1,7 +1,10 @@
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Shared Subtrees
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---------------
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.. SPDX-License-Identifier: GPL-2.0
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Contents:
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===============
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Shared Subtrees
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===============
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.. Contents:
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1) Overview
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2) Features
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3) Setting mount states
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@ -41,31 +44,38 @@ replicas continue to be exactly same.
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Here is an example:
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Let's say /mnt has a mount that is shared.
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mount --make-shared /mnt
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Let's say /mnt has a mount that is shared::
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mount --make-shared /mnt
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Note: mount(8) command now supports the --make-shared flag,
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so the sample 'smount' program is no longer needed and has been
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removed.
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# mount --bind /mnt /tmp
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::
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# mount --bind /mnt /tmp
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The above command replicates the mount at /mnt to the mountpoint /tmp
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and the contents of both the mounts remain identical.
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#ls /mnt
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a b c
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::
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#ls /tmp
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a b c
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#ls /mnt
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a b c
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Now let's say we mount a device at /tmp/a
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# mount /dev/sd0 /tmp/a
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#ls /tmp
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a b c
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#ls /tmp/a
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t1 t2 t3
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Now let's say we mount a device at /tmp/a::
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#ls /mnt/a
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t1 t2 t3
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# mount /dev/sd0 /tmp/a
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#ls /tmp/a
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t1 t2 t3
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#ls /mnt/a
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t1 t2 t3
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Note that the mount has propagated to the mount at /mnt as well.
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@ -123,14 +133,15 @@ replicas continue to be exactly same.
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2d) A unbindable mount is a unbindable private mount
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let's say we have a mount at /mnt and we make it unbindable
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let's say we have a mount at /mnt and we make it unbindable::
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# mount --make-unbindable /mnt
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# mount --make-unbindable /mnt
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Let's try to bind mount this mount somewhere else.
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# mount --bind /mnt /tmp
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mount: wrong fs type, bad option, bad superblock on /mnt,
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or too many mounted file systems
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Let's try to bind mount this mount somewhere else::
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# mount --bind /mnt /tmp
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mount: wrong fs type, bad option, bad superblock on /mnt,
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or too many mounted file systems
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Binding a unbindable mount is a invalid operation.
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@ -138,12 +149,12 @@ replicas continue to be exactly same.
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3) Setting mount states
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The mount command (util-linux package) can be used to set mount
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states:
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states::
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mount --make-shared mountpoint
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mount --make-slave mountpoint
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mount --make-private mountpoint
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mount --make-unbindable mountpoint
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mount --make-shared mountpoint
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mount --make-slave mountpoint
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mount --make-private mountpoint
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mount --make-unbindable mountpoint
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4) Use cases
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@ -154,9 +165,10 @@ replicas continue to be exactly same.
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Solution:
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The system administrator can make the mount at /cdrom shared
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mount --bind /cdrom /cdrom
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mount --make-shared /cdrom
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The system administrator can make the mount at /cdrom shared::
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mount --bind /cdrom /cdrom
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mount --make-shared /cdrom
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Now any process that clones off a new namespace will have a
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mount at /cdrom which is a replica of the same mount in the
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Solution:
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To begin with, the administrator can mark the entire mount tree
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as shareable.
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as shareable::
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mount --make-rshared /
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mount --make-rshared /
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A new process can clone off a new namespace. And mark some part
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of its namespace as slave
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of its namespace as slave::
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mount --make-rslave /myprivatetree
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mount --make-rslave /myprivatetree
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Hence forth any mounts within the /myprivatetree done by the
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process will not show up in any other namespace. However mounts
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@ -206,13 +218,13 @@ replicas continue to be exactly same.
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versions of the file depending on the path used to access that
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file.
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An example is:
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An example is::
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mount --make-shared /
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mount --rbind / /view/v1
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mount --rbind / /view/v2
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mount --rbind / /view/v3
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mount --rbind / /view/v4
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mount --make-shared /
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mount --rbind / /view/v1
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mount --rbind / /view/v2
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mount --rbind / /view/v3
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mount --rbind / /view/v4
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and if /usr has a versioning filesystem mounted, then that
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mount appears at /view/v1/usr, /view/v2/usr, /view/v3/usr and
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filesystem is being requested and return the corresponding
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inode.
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5) Detailed semantics:
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-------------------
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5) Detailed semantics
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---------------------
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The section below explains the detailed semantics of
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bind, rbind, move, mount, umount and clone-namespace operations.
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5a) Mount states
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A given mount can be in one of the following states
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1) shared
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2) slave
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3) shared and slave
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A 'shared mount' is defined as a vfsmount that belongs to a
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'peer group'.
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For example:
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For example::
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mount --make-shared /mnt
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mount --bind /mnt /tmp
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A slave mount as the name implies has a master mount from which
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mount/unmount events are received. Events do not propagate from
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the slave mount to the master. Only a shared mount can be made
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a slave by executing the following command
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a slave by executing the following command::
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mount --make-slave mount
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peer group.
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Only a slave vfsmount can be made as 'shared and slave' by
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either executing the following command
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either executing the following command::
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mount --make-shared mount
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or by moving the slave vfsmount under a shared vfsmount.
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(4) Private mount
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State diagram:
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The state diagram below explains the state transition of a mount,
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in response to various commands.
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------------------------------------------------------------------------
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| |make-shared | make-slave | make-private |make-unbindab|
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--------------|------------|--------------|--------------|-------------|
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|shared |shared |*slave/private| private | unbindable |
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| | | | | |
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|-------------|------------|--------------|--------------|-------------|
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|slave |shared | **slave | private | unbindable |
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| |and slave | | | |
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|-------------|------------|--------------|--------------|-------------|
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|shared |shared | slave | private | unbindable |
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|and slave |and slave | | | |
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|-------------|------------|--------------|--------------|-------------|
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|private |shared | **private | private | unbindable |
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|-------------|------------|--------------|--------------|-------------|
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|unbindable |shared |**unbindable | private | unbindable |
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------------------------------------------------------------------------
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in response to various commands::
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* if the shared mount is the only mount in its peer group, making it
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slave, makes it private automatically. Note that there is no master to
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which it can be slaved to.
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-----------------------------------------------------------------------
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| |make-shared | make-slave | make-private |make-unbindab|
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--------------|------------|--------------|--------------|-------------|
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|shared |shared |*slave/private| private | unbindable |
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| | | | | |
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|-------------|------------|--------------|--------------|-------------|
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|slave |shared | **slave | private | unbindable |
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| |and slave | | | |
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|-------------|------------|--------------|--------------|-------------|
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|shared |shared | slave | private | unbindable |
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|and slave |and slave | | | |
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|-------------|------------|--------------|--------------|-------------|
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|private |shared | **private | private | unbindable |
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|-------------|------------|--------------|--------------|-------------|
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|unbindable |shared |**unbindable | private | unbindable |
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------------------------------------------------------------------------
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** slaving a non-shared mount has no effect on the mount.
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* if the shared mount is the only mount in its peer group, making it
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slave, makes it private automatically. Note that there is no master to
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which it can be slaved to.
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** slaving a non-shared mount has no effect on the mount.
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Apart from the commands listed below, the 'move' operation also changes
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the state of a mount depending on type of the destination mount. Its
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5b) Bind semantics
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Consider the following command
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Consider the following command::
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mount --bind A/a B/b
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mount --bind A/a B/b
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where 'A' is the source mount, 'a' is the dentry in the mount 'A', 'B'
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is the destination mount and 'b' is the dentry in the destination mount.
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The outcome depends on the type of mount of 'A' and 'B'. The table
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below contains quick reference.
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---------------------------------------------------------------------------
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| BIND MOUNT OPERATION |
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|**************************************************************************
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|source(A)->| shared | private | slave | unbindable |
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| dest(B) | | | | |
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| | | | | | |
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| v | | | | |
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|**************************************************************************
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| shared | shared | shared | shared & slave | invalid |
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| | | | | |
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|non-shared| shared | private | slave | invalid |
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***************************************************************************
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below contains quick reference::
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--------------------------------------------------------------------------
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| BIND MOUNT OPERATION |
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|************************************************************************|
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|source(A)->| shared | private | slave | unbindable |
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| dest(B) | | | | |
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| | | | | | |
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| v | | | | |
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|************************************************************************|
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| shared | shared | shared | shared & slave | invalid |
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| | | | | |
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|non-shared| shared | private | slave | invalid |
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**************************************************************************
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Details:
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1. 'A' is a shared mount and 'B' is a shared mount. A new mount 'C'
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1. 'A' is a shared mount and 'B' is a shared mount. A new mount 'C'
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which is clone of 'A', is created. Its root dentry is 'a' . 'C' is
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mounted on mount 'B' at dentry 'b'. Also new mount 'C1', 'C2', 'C3' ...
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are created and mounted at the dentry 'b' on all mounts where 'B'
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'B'. And finally the peer-group of 'C' is merged with the peer group
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of 'A'.
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2. 'A' is a private mount and 'B' is a shared mount. A new mount 'C'
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2. 'A' is a private mount and 'B' is a shared mount. A new mount 'C'
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which is clone of 'A', is created. Its root dentry is 'a'. 'C' is
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mounted on mount 'B' at dentry 'b'. Also new mount 'C1', 'C2', 'C3' ...
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are created and mounted at the dentry 'b' on all mounts where 'B'
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'C', 'C1', .., 'Cn' with exactly the same configuration as the
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propagation tree for 'B'.
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3. 'A' is a slave mount of mount 'Z' and 'B' is a shared mount. A new
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3. 'A' is a slave mount of mount 'Z' and 'B' is a shared mount. A new
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mount 'C' which is clone of 'A', is created. Its root dentry is 'a' .
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'C' is mounted on mount 'B' at dentry 'b'. Also new mounts 'C1', 'C2',
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'C3' ... are created and mounted at the dentry 'b' on all mounts where
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@ -389,19 +408,19 @@ replicas continue to be exactly same.
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is made the slave of mount 'Z'. In other words, mount 'C' is in the
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state 'slave and shared'.
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4. 'A' is a unbindable mount and 'B' is a shared mount. This is a
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4. 'A' is a unbindable mount and 'B' is a shared mount. This is a
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invalid operation.
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5. 'A' is a private mount and 'B' is a non-shared(private or slave or
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5. 'A' is a private mount and 'B' is a non-shared(private or slave or
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unbindable) mount. A new mount 'C' which is clone of 'A', is created.
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Its root dentry is 'a'. 'C' is mounted on mount 'B' at dentry 'b'.
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6. 'A' is a shared mount and 'B' is a non-shared mount. A new mount 'C'
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6. 'A' is a shared mount and 'B' is a non-shared mount. A new mount 'C'
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which is a clone of 'A' is created. Its root dentry is 'a'. 'C' is
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mounted on mount 'B' at dentry 'b'. 'C' is made a member of the
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peer-group of 'A'.
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7. 'A' is a slave mount of mount 'Z' and 'B' is a non-shared mount. A
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7. 'A' is a slave mount of mount 'Z' and 'B' is a non-shared mount. A
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new mount 'C' which is a clone of 'A' is created. Its root dentry is
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'a'. 'C' is mounted on mount 'B' at dentry 'b'. Also 'C' is set as a
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slave mount of 'Z'. In other words 'A' and 'C' are both slave mounts of
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mount/unmount on 'A' do not propagate anywhere else. Similarly
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mount/unmount on 'C' do not propagate anywhere else.
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8. 'A' is a unbindable mount and 'B' is a non-shared mount. This is a
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8. 'A' is a unbindable mount and 'B' is a non-shared mount. This is a
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invalid operation. A unbindable mount cannot be bind mounted.
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5c) Rbind semantics
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@ -422,7 +441,9 @@ replicas continue to be exactly same.
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then the subtree under the unbindable mount is pruned in the new
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location.
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eg: let's say we have the following mount tree.
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eg:
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let's say we have the following mount tree::
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A
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/ \
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@ -430,12 +451,12 @@ replicas continue to be exactly same.
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/ \ / \
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D E F G
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Let's say all the mount except the mount C in the tree are
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of a type other than unbindable.
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Let's say all the mount except the mount C in the tree are
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of a type other than unbindable.
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If this tree is rbound to say Z
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If this tree is rbound to say Z
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We will have the following tree at the new location.
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We will have the following tree at the new location::
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Z
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|
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|
@ -457,24 +478,26 @@ replicas continue to be exactly same.
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the dentry in the destination mount.
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The outcome depends on the type of the mount of 'A' and 'B'. The table
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below is a quick reference.
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---------------------------------------------------------------------------
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| MOVE MOUNT OPERATION |
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|**************************************************************************
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| source(A)->| shared | private | slave | unbindable |
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| dest(B) | | | | |
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| | | | | | |
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| v | | | | |
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|**************************************************************************
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| shared | shared | shared |shared and slave| invalid |
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| | | | | |
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|non-shared| shared | private | slave | unbindable |
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***************************************************************************
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NOTE: moving a mount residing under a shared mount is invalid.
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below is a quick reference::
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---------------------------------------------------------------------------
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| MOVE MOUNT OPERATION |
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|**************************************************************************
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| source(A)->| shared | private | slave | unbindable |
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| dest(B) | | | | |
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| | | | | | |
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| v | | | | |
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|**************************************************************************
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| shared | shared | shared |shared and slave| invalid |
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| | | | | |
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|non-shared| shared | private | slave | unbindable |
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***************************************************************************
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.. Note:: moving a mount residing under a shared mount is invalid.
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Details follow:
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1. 'A' is a shared mount and 'B' is a shared mount. The mount 'A' is
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1. 'A' is a shared mount and 'B' is a shared mount. The mount 'A' is
|
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mounted on mount 'B' at dentry 'b'. Also new mounts 'A1', 'A2'...'An'
|
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are created and mounted at dentry 'b' on all mounts that receive
|
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propagation from mount 'B'. A new propagation tree is created in the
|
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|
@ -483,7 +506,7 @@ replicas continue to be exactly same.
|
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propagation tree is appended to the already existing propagation tree
|
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of 'A'.
|
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2. 'A' is a private mount and 'B' is a shared mount. The mount 'A' is
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2. 'A' is a private mount and 'B' is a shared mount. The mount 'A' is
|
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mounted on mount 'B' at dentry 'b'. Also new mount 'A1', 'A2'... 'An'
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are created and mounted at dentry 'b' on all mounts that receive
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propagation from mount 'B'. The mount 'A' becomes a shared mount and a
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||||
|
@ -491,7 +514,7 @@ replicas continue to be exactly same.
|
|||
'B'. This new propagation tree contains all the new mounts 'A1',
|
||||
'A2'... 'An'.
|
||||
|
||||
3. 'A' is a slave mount of mount 'Z' and 'B' is a shared mount. The
|
||||
3. 'A' is a slave mount of mount 'Z' and 'B' is a shared mount. The
|
||||
mount 'A' is mounted on mount 'B' at dentry 'b'. Also new mounts 'A1',
|
||||
'A2'... 'An' are created and mounted at dentry 'b' on all mounts that
|
||||
receive propagation from mount 'B'. A new propagation tree is created
|
||||
|
@ -501,32 +524,32 @@ replicas continue to be exactly same.
|
|||
'A'. Mount 'A' continues to be the slave mount of 'Z' but it also
|
||||
becomes 'shared'.
|
||||
|
||||
4. 'A' is a unbindable mount and 'B' is a shared mount. The operation
|
||||
4. 'A' is a unbindable mount and 'B' is a shared mount. The operation
|
||||
is invalid. Because mounting anything on the shared mount 'B' can
|
||||
create new mounts that get mounted on the mounts that receive
|
||||
propagation from 'B'. And since the mount 'A' is unbindable, cloning
|
||||
it to mount at other mountpoints is not possible.
|
||||
|
||||
5. 'A' is a private mount and 'B' is a non-shared(private or slave or
|
||||
5. 'A' is a private mount and 'B' is a non-shared(private or slave or
|
||||
unbindable) mount. The mount 'A' is mounted on mount 'B' at dentry 'b'.
|
||||
|
||||
6. 'A' is a shared mount and 'B' is a non-shared mount. The mount 'A'
|
||||
6. 'A' is a shared mount and 'B' is a non-shared mount. The mount 'A'
|
||||
is mounted on mount 'B' at dentry 'b'. Mount 'A' continues to be a
|
||||
shared mount.
|
||||
|
||||
7. 'A' is a slave mount of mount 'Z' and 'B' is a non-shared mount.
|
||||
7. 'A' is a slave mount of mount 'Z' and 'B' is a non-shared mount.
|
||||
The mount 'A' is mounted on mount 'B' at dentry 'b'. Mount 'A'
|
||||
continues to be a slave mount of mount 'Z'.
|
||||
|
||||
8. 'A' is a unbindable mount and 'B' is a non-shared mount. The mount
|
||||
8. 'A' is a unbindable mount and 'B' is a non-shared mount. The mount
|
||||
'A' is mounted on mount 'B' at dentry 'b'. Mount 'A' continues to be a
|
||||
unbindable mount.
|
||||
|
||||
5e) Mount semantics
|
||||
|
||||
Consider the following command
|
||||
Consider the following command::
|
||||
|
||||
mount device B/b
|
||||
mount device B/b
|
||||
|
||||
'B' is the destination mount and 'b' is the dentry in the destination
|
||||
mount.
|
||||
|
@ -537,9 +560,9 @@ replicas continue to be exactly same.
|
|||
|
||||
5f) Unmount semantics
|
||||
|
||||
Consider the following command
|
||||
Consider the following command::
|
||||
|
||||
umount A
|
||||
umount A
|
||||
|
||||
where 'A' is a mount mounted on mount 'B' at dentry 'b'.
|
||||
|
||||
|
@ -592,10 +615,12 @@ replicas continue to be exactly same.
|
|||
|
||||
A. What is the result of the following command sequence?
|
||||
|
||||
mount --bind /mnt /mnt
|
||||
mount --make-shared /mnt
|
||||
mount --bind /mnt /tmp
|
||||
mount --move /tmp /mnt/1
|
||||
::
|
||||
|
||||
mount --bind /mnt /mnt
|
||||
mount --make-shared /mnt
|
||||
mount --bind /mnt /tmp
|
||||
mount --move /tmp /mnt/1
|
||||
|
||||
what should be the contents of /mnt /mnt/1 /mnt/1/1 should be?
|
||||
Should they all be identical? or should /mnt and /mnt/1 be
|
||||
|
@ -604,23 +629,27 @@ replicas continue to be exactly same.
|
|||
|
||||
B. What is the result of the following command sequence?
|
||||
|
||||
mount --make-rshared /
|
||||
mkdir -p /v/1
|
||||
mount --rbind / /v/1
|
||||
::
|
||||
|
||||
mount --make-rshared /
|
||||
mkdir -p /v/1
|
||||
mount --rbind / /v/1
|
||||
|
||||
what should be the content of /v/1/v/1 be?
|
||||
|
||||
|
||||
C. What is the result of the following command sequence?
|
||||
|
||||
mount --bind /mnt /mnt
|
||||
mount --make-shared /mnt
|
||||
mkdir -p /mnt/1/2/3 /mnt/1/test
|
||||
mount --bind /mnt/1 /tmp
|
||||
mount --make-slave /mnt
|
||||
mount --make-shared /mnt
|
||||
mount --bind /mnt/1/2 /tmp1
|
||||
mount --make-slave /mnt
|
||||
::
|
||||
|
||||
mount --bind /mnt /mnt
|
||||
mount --make-shared /mnt
|
||||
mkdir -p /mnt/1/2/3 /mnt/1/test
|
||||
mount --bind /mnt/1 /tmp
|
||||
mount --make-slave /mnt
|
||||
mount --make-shared /mnt
|
||||
mount --bind /mnt/1/2 /tmp1
|
||||
mount --make-slave /mnt
|
||||
|
||||
At this point we have the first mount at /tmp and
|
||||
its root dentry is 1. Let's call this mount 'A'
|
||||
|
@ -668,7 +697,8 @@ replicas continue to be exactly same.
|
|||
|
||||
step 1:
|
||||
let's say the root tree has just two directories with
|
||||
one vfsmount.
|
||||
one vfsmount::
|
||||
|
||||
root
|
||||
/ \
|
||||
tmp usr
|
||||
|
@ -676,14 +706,17 @@ replicas continue to be exactly same.
|
|||
And we want to replicate the tree at multiple
|
||||
mountpoints under /root/tmp
|
||||
|
||||
step2:
|
||||
mount --make-shared /root
|
||||
step 2:
|
||||
::
|
||||
|
||||
mkdir -p /tmp/m1
|
||||
|
||||
mount --rbind /root /tmp/m1
|
||||
mount --make-shared /root
|
||||
|
||||
the new tree now looks like this:
|
||||
mkdir -p /tmp/m1
|
||||
|
||||
mount --rbind /root /tmp/m1
|
||||
|
||||
the new tree now looks like this::
|
||||
|
||||
root
|
||||
/ \
|
||||
|
@ -697,11 +730,13 @@ replicas continue to be exactly same.
|
|||
|
||||
it has two vfsmounts
|
||||
|
||||
step3:
|
||||
step 3:
|
||||
::
|
||||
|
||||
mkdir -p /tmp/m2
|
||||
mount --rbind /root /tmp/m2
|
||||
|
||||
the new tree now looks like this:
|
||||
the new tree now looks like this::
|
||||
|
||||
root
|
||||
/ \
|
||||
|
@ -724,6 +759,7 @@ replicas continue to be exactly same.
|
|||
it has 6 vfsmounts
|
||||
|
||||
step 4:
|
||||
::
|
||||
mkdir -p /tmp/m3
|
||||
mount --rbind /root /tmp/m3
|
||||
|
||||
|
@ -740,7 +776,8 @@ replicas continue to be exactly same.
|
|||
|
||||
step 1:
|
||||
let's say the root tree has just two directories with
|
||||
one vfsmount.
|
||||
one vfsmount::
|
||||
|
||||
root
|
||||
/ \
|
||||
tmp usr
|
||||
|
@ -748,17 +785,20 @@ replicas continue to be exactly same.
|
|||
How do we set up the same tree at multiple locations under
|
||||
/root/tmp
|
||||
|
||||
step2:
|
||||
mount --bind /root/tmp /root/tmp
|
||||
step 2:
|
||||
::
|
||||
|
||||
mount --make-rshared /root
|
||||
mount --make-unbindable /root/tmp
|
||||
|
||||
mkdir -p /tmp/m1
|
||||
mount --bind /root/tmp /root/tmp
|
||||
|
||||
mount --rbind /root /tmp/m1
|
||||
mount --make-rshared /root
|
||||
mount --make-unbindable /root/tmp
|
||||
|
||||
the new tree now looks like this:
|
||||
mkdir -p /tmp/m1
|
||||
|
||||
mount --rbind /root /tmp/m1
|
||||
|
||||
the new tree now looks like this::
|
||||
|
||||
root
|
||||
/ \
|
||||
|
@ -768,11 +808,13 @@ replicas continue to be exactly same.
|
|||
/ \
|
||||
tmp usr
|
||||
|
||||
step3:
|
||||
step 3:
|
||||
::
|
||||
|
||||
mkdir -p /tmp/m2
|
||||
mount --rbind /root /tmp/m2
|
||||
|
||||
the new tree now looks like this:
|
||||
the new tree now looks like this::
|
||||
|
||||
root
|
||||
/ \
|
||||
|
@ -782,12 +824,13 @@ replicas continue to be exactly same.
|
|||
/ \ / \
|
||||
tmp usr tmp usr
|
||||
|
||||
step4:
|
||||
step 4:
|
||||
::
|
||||
|
||||
mkdir -p /tmp/m3
|
||||
mount --rbind /root /tmp/m3
|
||||
|
||||
the new tree now looks like this:
|
||||
the new tree now looks like this::
|
||||
|
||||
root
|
||||
/ \
|
||||
|
@ -801,25 +844,31 @@ replicas continue to be exactly same.
|
|||
|
||||
8A) Datastructure
|
||||
|
||||
4 new fields are introduced to struct vfsmount
|
||||
->mnt_share
|
||||
->mnt_slave_list
|
||||
->mnt_slave
|
||||
->mnt_master
|
||||
4 new fields are introduced to struct vfsmount:
|
||||
|
||||
->mnt_share links together all the mount to/from which this vfsmount
|
||||
* ->mnt_share
|
||||
* ->mnt_slave_list
|
||||
* ->mnt_slave
|
||||
* ->mnt_master
|
||||
|
||||
->mnt_share
|
||||
links together all the mount to/from which this vfsmount
|
||||
send/receives propagation events.
|
||||
|
||||
->mnt_slave_list links all the mounts to which this vfsmount propagates
|
||||
->mnt_slave_list
|
||||
links all the mounts to which this vfsmount propagates
|
||||
to.
|
||||
|
||||
->mnt_slave links together all the slaves that its master vfsmount
|
||||
->mnt_slave
|
||||
links together all the slaves that its master vfsmount
|
||||
propagates to.
|
||||
|
||||
->mnt_master points to the master vfsmount from which this vfsmount
|
||||
->mnt_master
|
||||
points to the master vfsmount from which this vfsmount
|
||||
receives propagation.
|
||||
|
||||
->mnt_flags takes two more flags to indicate the propagation status of
|
||||
->mnt_flags
|
||||
takes two more flags to indicate the propagation status of
|
||||
the vfsmount. MNT_SHARE indicates that the vfsmount is a shared
|
||||
vfsmount. MNT_UNCLONABLE indicates that the vfsmount cannot be
|
||||
replicated.
|
||||
|
@ -842,7 +891,7 @@ replicas continue to be exactly same.
|
|||
|
||||
A example propagation tree looks as shown in the figure below.
|
||||
[ NOTE: Though it looks like a forest, if we consider all the shared
|
||||
mounts as a conceptual entity called 'pnode', it becomes a tree]
|
||||
mounts as a conceptual entity called 'pnode', it becomes a tree]::
|
||||
|
||||
|
||||
A <--> B <--> C <---> D
|
||||
|
@ -864,14 +913,19 @@ replicas continue to be exactly same.
|
|||
A's ->mnt_slave_list links with ->mnt_slave of 'E', 'K', 'F' and 'G'
|
||||
|
||||
E's ->mnt_share links with ->mnt_share of K
|
||||
'E', 'K', 'F', 'G' have their ->mnt_master point to struct
|
||||
vfsmount of 'A'
|
||||
|
||||
'E', 'K', 'F', 'G' have their ->mnt_master point to struct vfsmount of 'A'
|
||||
|
||||
'M', 'L', 'N' have their ->mnt_master point to struct vfsmount of 'K'
|
||||
|
||||
K's ->mnt_slave_list links with ->mnt_slave of 'M', 'L' and 'N'
|
||||
|
||||
C's ->mnt_slave_list links with ->mnt_slave of 'J' and 'K'
|
||||
|
||||
J and K's ->mnt_master points to struct vfsmount of C
|
||||
|
||||
and finally D's ->mnt_slave_list links with ->mnt_slave of 'H' and 'I'
|
||||
|
||||
'H' and 'I' have their ->mnt_master pointing to struct vfsmount of 'D'.
|
||||
|
||||
|
||||
|
@ -903,6 +957,7 @@ replicas continue to be exactly same.
|
|||
Prepare phase:
|
||||
|
||||
for each mount in the source tree:
|
||||
|
||||
a) Create the necessary number of mount trees to
|
||||
be attached to each of the mounts that receive
|
||||
propagation from the destination mount.
|
||||
|
@ -929,11 +984,12 @@ replicas continue to be exactly same.
|
|||
Abort phase
|
||||
delete all the newly created trees.
|
||||
|
||||
NOTE: all the propagation related functionality resides in the file
|
||||
pnode.c
|
||||
.. Note::
|
||||
all the propagation related functionality resides in the file pnode.c
|
||||
|
||||
|
||||
------------------------------------------------------------------------
|
||||
|
||||
version 0.1 (created the initial document, Ram Pai linuxram@us.ibm.com)
|
||||
|
||||
version 0.2 (Incorporated comments from Al Viro)
|
Loading…
Reference in New Issue
Block a user