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binderfs: reserve devices for initial mount

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The binderfs instance in the initial ipc namespace will always have a
reserve of 4 binder devices unless explicitly capped by specifying a lower
value via the "max" mount option.
This ensures when binder devices are removed (on accident or on purpose)
they can always be recreated without risking that all minor numbers have
already been used up.

Cc: Todd Kjos <tkjos@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Christian Brauner 2019-01-11 11:19:40 +01:00 committed by Greg Kroah-Hartman
parent c13295ad21
commit 36bdf3cae0
1 changed files with 6 additions and 1 deletions
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7
drivers/android/binderfs.c
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@ -40,6 +40,8 @@
#define INODE_OFFSET 3
#define INTSTRLEN 21
#define BINDERFS_MAX_MINOR (1U << MINORBITS)
/* Ensure that the initial ipc namespace always has devices available. */
#define BINDERFS_MAX_MINOR_CAPPED (BINDERFS_MAX_MINOR - 4)
static dev_t binderfs_dev;
static DEFINE_MUTEX(binderfs_minors_mutex);
@ -127,11 +129,14 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
struct inode *inode = NULL;
struct super_block *sb = ref_inode->i_sb;
struct binderfs_info *info = sb->s_fs_info;
bool use_reserve = (info->ipc_ns == &init_ipc_ns);
/* Reserve new minor number for the new device. */
mutex_lock(&binderfs_minors_mutex);
if (++info->device_count <= info->mount_opts.max)
minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR,
minor = ida_alloc_max(&binderfs_minors,
use_reserve ? BINDERFS_MAX_MINOR :
BINDERFS_MAX_MINOR_CAPPED,
GFP_KERNEL);
else
minor = -ENOSPC;