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Message-ID: <157117620241.15019.14840217828666282360.stgit@warthog.procyon.org.uk>
Date: Tue, 15 Oct 2019 22:50:02 +0100
From: David Howells <dhowells@...hat.com>
To: torvalds@...ux-foundation.org
Cc: dhowells@...hat.com, Casey Schaufler <casey@...aufler-ca.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
nicolas.dichtel@...nd.com, raven@...maw.net,
Christian Brauner <christian@...uner.io>, dhowells@...hat.com,
keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
linux-block@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 15/21] pipe: Allow buffers to be marked
read-whole-or-error for notifications
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 <dhowells@...hat.com>
---
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];
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