[PATCH v3] media: vb2: use ssize_t for vb2_read/vb2_write

[Zile Xiong <xiongzile99@gmail.com>]

vb2_read() and vb2_write() return size_t, but propagate
negative errno values from __vb2_perform_fileio() via
implicit signed/unsigned conversions in callers
(e.g. vb2_fop_read()), which is not obvious.

vb2_fop_read() and vb2_fop_write() already return ssize_t, so
using size_t for vb2_read(), vb2_write(), and
__vb2_perform_fileio() is inconsistent.

Switch these helpers to ssize_t so they can return either a byte
count or a negative error code.

Fixes: b25748fe6126 ("[media] v4l: videobuf2: add read() and write() emulator")
Cc: stable@vger.kernel.org
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Zile Xiong <xiongzile99@gmail.com>
---
v3:
- add Cc: stable@vger.kernel.org
- fix function argument alignment

v2:
- add Fixes tag
- clarify type consistency with vb2_fop_read/write
---
 drivers/media/common/videobuf2/videobuf2-core.c | 13 +++++++------
 include/media/videobuf2-core.h                  |  8 ++++----
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index adf668b213c2..d5c3d4d939aa 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -2990,8 +2990,9 @@ static int __vb2_cleanup_fileio(struct vb2_queue *q)
  * @nonblock:	mode selector (1 means blocking calls, 0 means nonblocking)
  * @read:	access mode selector (1 means read, 0 means write)
  */
-static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_t count,
-		loff_t *ppos, int nonblock, int read)
+static ssize_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data,
+				    size_t count, loff_t *ppos,
+				    int nonblock, int read)
 {
 	struct vb2_fileio_data *fileio;
 	struct vb2_fileio_buf *buf;
@@ -3154,15 +3155,15 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
 	return ret;
 }
 
-size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
-		loff_t *ppos, int nonblocking)
+ssize_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
+		 loff_t *ppos, int nonblocking)
 {
 	return __vb2_perform_fileio(q, data, count, ppos, nonblocking, 1);
 }
 EXPORT_SYMBOL_GPL(vb2_read);
 
-size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
-		loff_t *ppos, int nonblocking)
+ssize_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
+		  loff_t *ppos, int nonblocking)
 {
 	return __vb2_perform_fileio(q, (char __user *) data, count,
 							ppos, nonblocking, 0);
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 4424d481d7f7..4b4f4c15c53a 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -1093,8 +1093,8 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file,
  * @ppos:	file handle position tracking pointer
  * @nonblock:	mode selector (1 means blocking calls, 0 means nonblocking)
  */
-size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
-		loff_t *ppos, int nonblock);
+ssize_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
+		 loff_t *ppos, int nonblock);
 /**
  * vb2_write() - implements write() syscall logic.
  * @q:		pointer to &struct vb2_queue with videobuf2 queue.
@@ -1103,8 +1103,8 @@ size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
  * @ppos:	file handle position tracking pointer
  * @nonblock:	mode selector (1 means blocking calls, 0 means nonblocking)
  */
-size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
-		loff_t *ppos, int nonblock);
+ssize_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
+		  loff_t *ppos, int nonblock);
 
 /**
  * typedef vb2_thread_fnc - callback function for use with vb2_thread.
-- 
2.39.5