Allow a buffer to be marked such that read() must return the entire buffer in one go or return ENOBUFS. Multiple buffers can be amalgamated into a single read, but a short read will occur if the next "whole" buffer won't fit.
This is useful for watch queue notifications to make sure we don't split a notification across multiple reads, especially given that we need to fabricate an overrun record under some circumstances - and that isn't in the buffers. Signed-off-by: David Howells <[email protected]> --- fs/pipe.c | 8 +++++++- include/linux/pipe_fs_i.h | 1 + kernel/watch_queue.c | 2 +- samples/watch_queue/watch_test.c | 2 +- 4 files changed, 10 insertions(+), 3 deletions(-) diff --git a/fs/pipe.c b/fs/pipe.c index d385e3a5492e..f4c9d5480636 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -297,8 +297,14 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) size_t written; int error; - if (chars > total_len) + if (chars > total_len) { + if (buf->flags & PIPE_BUF_FLAG_WHOLE) { + if (ret == 0) + ret = -ENOBUFS; + break; + } chars = total_len; + } error = pipe_buf_confirm(pipe, buf); if (error) { diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index e42a98d98c3d..58583ba056e8 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -8,6 +8,7 @@ #define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */ #define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */ #define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */ +#define PIPE_BUF_FLAG_WHOLE 0x10 /* read() must return entire buffer or error */ /** * struct pipe_buffer - a linux kernel pipe buffer diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index 40dae7dda6d6..f1d78da5309d 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -115,7 +115,7 @@ static bool post_one_notification(struct watch_queue *wqueue, buf->ops = &watch_queue_pipe_buf_ops; buf->offset = offset; buf->len = len; - buf->flags = 0; + buf->flags = PIPE_BUF_FLAG_WHOLE; pipe_commit_write(pipe, head + 1); if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c index 19b82e9b0853..363f1d77386f 100644 --- a/samples/watch_queue/watch_test.c +++ b/samples/watch_queue/watch_test.c @@ -64,7 +64,7 @@ static void saw_key_change(struct watch_notification *n, size_t len) */ static void consumer(int fd) { - unsigned char buffer[4096], *p, *end; + unsigned char buffer[433], *p, *end; union { struct watch_notification n; unsigned char buf1[128];
