media: vb2: use ssize_t for vb2_read/vb2_write

vb2_read() and vb2_write() return size_t, but propagate
negative errno values from __vb2_perform_fileio().

This relies on implicit signed/unsigned conversions in callers
(e.g. vb2_fop_read()) to recover error codes:

    __vb2_perform_fileio() -> -EINVAL
    vb2_read()             -> (size_t)-EINVAL
    vb2_fop_read()         -> -EINVAL

This relies on implicit conversions that are not obvious.

These helpers are exported (EXPORT_SYMBOL_GPL) and part of the
vb2 API, so changing their return type may affect existing users.

However, they conceptually follow read/write semantics, where
ssize_t is typically used to return either a byte count or a
negative error code.

Switch vb2_read() and vb2_write() to ssize_t, and update
__vb2_perform_fileio() accordingly.

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

2 files changed, 10 insertions, 10 deletions

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index adf668b213c2..b0a6084f1757 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -2990,8 +2990,8 @@ 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 +3154,15 @@ 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.