lkml.org 
[lkml]   [2019]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[RFC v2 1/3] dma-buf: give each buffer a full-fledged inode
From
From: Greg Hackmann <ghackmann@google.com>

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>
---
drivers/dma-buf/dma-buf.c | 63 ++++++++++++++++++++++++++++++++++----
include/uapi/linux/magic.h | 1 +
2 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 7c858020d14b..ffd5a2ad7d6f 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -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;
@@ -338,6 +359,31 @@ 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
*
@@ -433,8 +479,7 @@ 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;
@@ -1025,8 +1070,8 @@ 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);
@@ -1037,11 +1082,12 @@ 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) {
@@ -1136,6 +1182,10 @@ 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();
@@ -1146,5 +1196,6 @@ 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);
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index f8c00045d537..665e18627f78 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -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__ */
--
2.21.0.225.g810b269d1ac-goog
\
 
 \ /
  Last update: 2019-03-22 03:52    [W:0.091 / U:34.004 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site