• Slavomir Kaslev's avatar
    fs: Make splice() and tee() take into account O_NONBLOCK flag on pipes · ee5e0011
    Slavomir Kaslev authored
    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#L1425Signed-off-by: 's avatarSlavomir Kaslev <kaslevs@vmware.com>
    Reviewed-by: 's avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    ee5e0011
Name
Last commit
Last update
..
9p Loading commit data...
adfs Loading commit data...
affs Loading commit data...
afs Loading commit data...
autofs Loading commit data...
befs Loading commit data...
bfs Loading commit data...
btrfs Loading commit data...
cachefiles Loading commit data...
ceph Loading commit data...
cifs Loading commit data...
coda Loading commit data...
configfs Loading commit data...
cramfs Loading commit data...
crypto Loading commit data...
debugfs Loading commit data...
devpts Loading commit data...
dlm Loading commit data...
ecryptfs Loading commit data...
efivarfs Loading commit data...
efs Loading commit data...
exofs Loading commit data...
exportfs Loading commit data...
ext2 Loading commit data...
ext4 Loading commit data...
f2fs Loading commit data...
fat Loading commit data...
freevxfs Loading commit data...
fscache Loading commit data...
fuse Loading commit data...
gfs2 Loading commit data...
hfs Loading commit data...
hfsplus Loading commit data...
hostfs Loading commit data...
hpfs Loading commit data...
hugetlbfs Loading commit data...
isofs Loading commit data...
jbd2 Loading commit data...
jffs2 Loading commit data...
jfs Loading commit data...
kernfs Loading commit data...
lockd Loading commit data...
minix Loading commit data...
nfs Loading commit data...
nfs_common Loading commit data...
nfsd Loading commit data...
nilfs2 Loading commit data...
nls Loading commit data...
notify Loading commit data...
ntfs Loading commit data...
ocfs2 Loading commit data...
omfs Loading commit data...
openpromfs Loading commit data...
orangefs Loading commit data...
overlayfs Loading commit data...
proc Loading commit data...
pstore Loading commit data...
qnx4 Loading commit data...
qnx6 Loading commit data...
quota Loading commit data...
ramfs Loading commit data...
reiserfs Loading commit data...
romfs Loading commit data...
squashfs Loading commit data...
sysfs Loading commit data...
sysv Loading commit data...
tracefs Loading commit data...
ubifs Loading commit data...
udf Loading commit data...
ufs Loading commit data...
xfs Loading commit data...
Kconfig Loading commit data...
Kconfig.binfmt Loading commit data...
Makefile Loading commit data...
aio.c Loading commit data...
anon_inodes.c Loading commit data...
attr.c Loading commit data...
bad_inode.c Loading commit data...
binfmt_aout.c Loading commit data...
binfmt_elf.c Loading commit data...
binfmt_elf_fdpic.c Loading commit data...
binfmt_em86.c Loading commit data...
binfmt_flat.c Loading commit data...
binfmt_misc.c Loading commit data...
binfmt_script.c Loading commit data...
block_dev.c Loading commit data...
buffer.c Loading commit data...
char_dev.c Loading commit data...
compat.c Loading commit data...
compat_binfmt_elf.c Loading commit data...
compat_ioctl.c Loading commit data...
coredump.c Loading commit data...
d_path.c Loading commit data...
dax.c Loading commit data...
dcache.c Loading commit data...
dcookies.c Loading commit data...
direct-io.c Loading commit data...
drop_caches.c Loading commit data...
eventfd.c Loading commit data...
eventpoll.c Loading commit data...
exec.c Loading commit data...
fcntl.c Loading commit data...
fhandle.c Loading commit data...
file.c Loading commit data...
file_table.c Loading commit data...
filesystems.c Loading commit data...
fs-writeback.c Loading commit data...
fs_pin.c Loading commit data...
fs_struct.c Loading commit data...
inode.c Loading commit data...
internal.h Loading commit data...
ioctl.c Loading commit data...
iomap.c Loading commit data...
libfs.c Loading commit data...
locks.c Loading commit data...
mbcache.c Loading commit data...
mount.h Loading commit data...
mpage.c Loading commit data...
namei.c Loading commit data...
namespace.c Loading commit data...
no-block.c Loading commit data...
nsfs.c Loading commit data...
open.c Loading commit data...
pipe.c Loading commit data...
pnode.c Loading commit data...
pnode.h Loading commit data...
posix_acl.c Loading commit data...
proc_namespace.c Loading commit data...
read_write.c Loading commit data...
readdir.c Loading commit data...
select.c Loading commit data...
seq_file.c Loading commit data...
signalfd.c Loading commit data...
splice.c Loading commit data...
stack.c Loading commit data...
stat.c Loading commit data...
statfs.c Loading commit data...
super.c Loading commit data...
sync.c Loading commit data...
timerfd.c Loading commit data...
userfaultfd.c Loading commit data...
utimes.c Loading commit data...
xattr.c Loading commit data...