[PATCH v3 2/2] dmabuf: Add dmabuf inode number to /proc/*/fdinfo

[Kalesh Singh <kaleshsingh@google.com>]

If a FD refers to a DMA buffer add the DMA buffer inode number to
/proc/<pid>/fdinfo/<FD> and /proc/<pid>/task/<tid>/fdindo/<FD>.

The dmabuf inode number allows userspace to uniquely identify the buffer
and avoids a dependency on /proc/<pid>/fd/* when accounting per-process
DMA buffer sizes.

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
Changes in v3:
  - Add documentation in proc.rst
Changes in v2:
  - Update patch description

 Documentation/filesystems/proc.rst | 17 +++++++++++++++++
 drivers/dma-buf/dma-buf.c          |  1 +
 2 files changed, 18 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2fa69f710e2a..fdd38676f57f 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -2031,6 +2031,23 @@ details]. 'it_value' is remaining time until the timer expiration.
 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
 still exhibits timer's remaining time.
 
+DMA Buffer files
+~~~~~~~~~~~~~~~~
+
+::
+
+	pos:	0
+	flags:	04002
+	mnt_id:	9
+	dmabuf_inode_no: 63107
+	size:   32768
+	count:  2
+	exp_name:  system-heap
+
+where 'dmabuf_inode_no' is the unique inode number of the DMA buffer file.
+'size' is the size of the DMA buffer in bytes. 'count' is the file count of
+the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
+
 3.9	/proc/<pid>/map_files - Information about memory mapped files
 ---------------------------------------------------------------------
 This directory contains symbolic links which represent memory mapped files
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 9ad6397aaa97..d869099ede83 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -414,6 +414,7 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
 {
 	struct dma_buf *dmabuf = file->private_data;
 
+	seq_printf(m, "dmabuf_inode_no:\t%lu\n", file_inode(file)->i_ino);
 	seq_printf(m, "size:\t%zu\n", dmabuf->size);
 	/* Don't count the temporary reference taken inside procfs seq_show */
 	seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
-- 
2.30.0.478.g8a0d178c01-goog