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dma-buf: give each buffer a full-fledged inode

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By traversing /proc/*/fd and /proc/*/map_files, processes with CAP_ADMIN
can get a lot of fine-grained data about how shmem buffers are shared
among processes.  stat(2) on each entry gives the caller a unique
ID (st_ino), the buffer's size (st_size), and even the number of pages
currently charged to the buffer (st_blocks / 512).

In contrast, all dma-bufs share the same anonymous inode.  So while we
can count how many dma-buf fds or mappings a process has, we can't get
the size of the backing buffers or tell if two entries point to the same
dma-buf.  On systems with debugfs, we can get a per-buffer breakdown of
size and reference count, but can't tell which processes are actually
holding the references to each buffer.

Replace the singleton inode with full-fledged inodes allocated by
alloc_anon_inode().  This involves creating and mounting a
mini-pseudo-filesystem for dma-buf, following the example in fs/aio.c.

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Chenbo Feng <fengc@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613223408.139221-2-fengc@google.com
This commit is contained in:
Greg Hackmann 2019-06-13 15:34:06 -07:00 committed by Sumit Semwal
parent 51e857af9f
commit ed63bb1d1f
2 changed files with 58 additions and 6 deletions
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63
drivers/dma-buf/dma-buf.c
View File

@ -34,8 +34,10 @@
#include <linux/poll.h>
#include <linux/reservation.h>
#include <linux/mm.h>
#include <linux/mount.h>
#include <uapi/linux/dma-buf.h>
#include <uapi/linux/magic.h>
static inline int is_dma_buf_file(struct file *);
@ -46,6 +48,25 @@ struct dma_buf_list {
static struct dma_buf_list db_list;
static const struct dentry_operations dma_buf_dentry_ops = {
.d_dname = simple_dname,
};
static struct vfsmount *dma_buf_mnt;
static struct dentry *dma_buf_fs_mount(struct file_system_type *fs_type,
int flags, const char *name, void *data)
{
return mount_pseudo(fs_type, "dmabuf:", NULL, &dma_buf_dentry_ops,
DMA_BUF_MAGIC);
}
static struct file_system_type dma_buf_fs_type = {
.name = "dmabuf",
.mount = dma_buf_fs_mount,
.kill_sb = kill_anon_super,
};
static int dma_buf_release(struct inode *inode, struct file *file)
{
struct dma_buf *dmabuf;
@ -342,6 +363,31 @@ static inline int is_dma_buf_file(struct file *file)
return file->f_op == &dma_buf_fops;
}
static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
{
struct file *file;
struct inode *inode = alloc_anon_inode(dma_buf_mnt->mnt_sb);
if (IS_ERR(inode))
return ERR_CAST(inode);
inode->i_size = dmabuf->size;
inode_set_bytes(inode, dmabuf->size);
file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf",
flags, &dma_buf_fops);
if (IS_ERR(file))
goto err_alloc_file;
file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
file->private_data = dmabuf;
return file;
err_alloc_file:
iput(inode);
return file;
}
/**
* DOC: dma buf device access
*
@ -436,8 +482,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
}
dmabuf->resv = resv;
file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf,
exp_info->flags);
file = dma_buf_getfile(dmabuf, exp_info->flags);
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto err_dmabuf;
@ -1055,8 +1100,8 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
return ret;
seq_puts(s, "\nDma-buf Objects:\n");
seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\n",
"size", "flags", "mode", "count");
seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\t%-8s\n",
"size", "flags", "mode", "count", "ino");
list_for_each_entry(buf_obj, &db_list.head, list_node) {
ret = mutex_lock_interruptible(&buf_obj->lock);
@ -1067,11 +1112,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
continue;
}
seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\n",
seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\n",
buf_obj->size,
buf_obj->file->f_flags, buf_obj->file->f_mode,
file_count(buf_obj->file),
buf_obj->exp_name);
buf_obj->exp_name,
file_inode(buf_obj->file)->i_ino);
robj = buf_obj->resv;
while (true) {
@ -1167,6 +1213,10 @@ static inline void dma_buf_uninit_debugfs(void)
static int __init dma_buf_init(void)
{
dma_buf_mnt = kern_mount(&dma_buf_fs_type);
if (IS_ERR(dma_buf_mnt))
return PTR_ERR(dma_buf_mnt);
mutex_init(&db_list.lock);
INIT_LIST_HEAD(&db_list.head);
dma_buf_init_debugfs();
@ -1177,5 +1227,6 @@ subsys_initcall(dma_buf_init);
static void __exit dma_buf_deinit(void)
{
dma_buf_uninit_debugfs();
kern_unmount(dma_buf_mnt);
}
__exitcall(dma_buf_deinit);

1
include/uapi/linux/magic.h
View File

@ -91,5 +91,6 @@
#define UDF_SUPER_MAGIC 0x15013346
#define BALLOON_KVM_MAGIC 0x13661366
#define ZSMALLOC_MAGIC 0x58295829
#define DMA_BUF_MAGIC 0x444d4142 /* "DMAB" */
#endif /* __LINUX_MAGIC_H__ */