diff options
authorSlavomir Kaslev <kaslevs@vmware.com>2019-02-07 17:45:19 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2019-03-04 16:10:17 -0800
commitee5e001196d1345b8fee25925ff5f1d67936081e (patch)
parentMerge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs (diff)
fs: Make splice() and tee() take into account O_NONBLOCK flag on pipes
The current implementation of splice() and tee() ignores O_NONBLOCK set on pipe file descriptors and checks only the SPLICE_F_NONBLOCK flag for blocking on pipe arguments. This is inconsistent since splice()-ing from/to non-pipe file descriptors does take O_NONBLOCK into consideration. Fix this by promoting O_NONBLOCK, when set on a pipe, to SPLICE_F_NONBLOCK. Some context for how the current implementation of splice() leads to inconsistent behavior. In the ongoing work[1] to add VM tracing capability to trace-cmd we stream tracing data over named FIFOs or vsockets from guests back to the host. When we receive SIGINT from user to stop tracing, we set O_NONBLOCK on the input file descriptor and set SPLICE_F_NONBLOCK for the next call to splice(). If splice() was blocked waiting on data from the input FIFO, after SIGINT splice() restarts with the same arguments (no SPLICE_F_NONBLOCK) and blocks again instead of returning -EAGAIN when no data is available. This differs from the splice() behavior when reading from a vsocket or when we're doing a traditional read()/write() loop (trace-cmd's --nosplice argument). With this patch applied we get the same behavior in all situations after setting O_NONBLOCK which also matches the behavior of doing a read()/write() loop instead of splice(). This change does have potential of breaking users who don't expect EAGAIN from splice() when SPLICE_F_NONBLOCK is not set. OTOH programs that set O_NONBLOCK and don't anticipate EAGAIN are arguably buggy[2]. [1] https://github.com/skaslev/trace-cmd/tree/vsock [2] https://github.com/torvalds/linux/blob/d47e3da1759230e394096fd742aad423c291ba48/fs/read_write.c#L1425 Signed-off-by: Slavomir Kaslev <kaslevs@vmware.com> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 12 insertions, 0 deletions
diff --git a/fs/splice.c b/fs/splice.c
index ec8b54b5c0d2..6489fb9436e4 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1123,6 +1123,9 @@ static long do_splice(struct file *in, loff_t __user *off_in,
if (ipipe == opipe)
return -EINVAL;
+ if ((in->f_flags | out->f_flags) & O_NONBLOCK)
return splice_pipe_to_pipe(ipipe, opipe, len, flags);
@@ -1148,6 +1151,9 @@ static long do_splice(struct file *in, loff_t __user *off_in,
if (unlikely(ret < 0))
return ret;
+ if (in->f_flags & O_NONBLOCK)
ret = do_splice_from(ipipe, out, &offset, len, flags);
@@ -1172,6 +1178,9 @@ static long do_splice(struct file *in, loff_t __user *off_in,
offset = in->f_pos;
+ if (out->f_flags & O_NONBLOCK)
ret = wait_for_space(opipe, flags);
if (!ret)
@@ -1717,6 +1726,9 @@ static long do_tee(struct file *in, struct file *out, size_t len,
* copying the data.
if (ipipe && opipe && ipipe != opipe) {
+ if ((in->f_flags | out->f_flags) & O_NONBLOCK)
* Keep going, unless we encounter an error. The ipipe/opipe
* ordering doesn't really matter.