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9883035ae7
linux/fs
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Linus Torvalds 9883035ae7 pipes: add a "packetized pipe" mode for writing 
The actual internal pipe implementation is already really about
individual packets (called "pipe buffers"), and this simply exposes that
as a special packetized mode.

When we are in the packetized mode (marked by O_DIRECT as suggested by
Alan Cox), a write() on a pipe will not merge the new data with previous
writes, so each write will get a pipe buffer of its own.  The pipe
buffer is then marked with the PIPE_BUF_FLAG_PACKET flag, which in turn
will tell the reader side to break the read at that boundary (and throw
away any partial packet contents that do not fit in the read buffer).

End result: as long as you do writes less than PIPE_BUF in size (so that
the pipe doesn't have to split them up), you can now treat the pipe as a
packet interface, where each read() system call will read one packet at
a time.  You can just use a sufficiently big read buffer (PIPE_BUF is
sufficient, since bigger than that doesn't guarantee atomicity anyway),
and the return value of the read() will naturally give you the size of
the packet.

NOTE! We do not support zero-sized packets, and zero-sized reads and
writes to a pipe continue to be no-ops.  Also note that big packets will
currently be split at write time, but that the size at which that
happens is not really specified (except that it's bigger than PIPE_BUF).
Currently that limit is the system page size, but we might want to
explicitly support bigger packets some day.

The main user for this is going to be the autofs packet interface,
allowing us to stop having to care so deeply about exact packet sizes
(which have had bugs with 32/64-bit compatibility modes).  But user
space can create packetized pipes with "pipe2(fd, O_DIRECT)", which will
fail with an EINVAL on kernels that do not support this interface.

Tested-by: Michael Tokarev <mjt@tls.msk.ru>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Miller <davem@davemloft.net>
Cc: Ian Kent <raven@themaw.net>
Cc: Thomas Meyer <thomas@m3y3r.de>
Cc: stable@kernel.org  # needed for systemd/autofs interaction fix
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-04-29 13:12:42 -07:00
..
9p 9p changes for the 3.4 merge window 2012-03-28 09:58:38 -07:00
adfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
affs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
afs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
autofs4 Revert "autofs: work around unhappy compat problem on x86-64" 2012-04-28 08:29:56 -07:00
befs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
bfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
btrfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs 2012-04-28 09:30:07 -07:00
cachefiles switch touch_atime to struct path 2012-03-20 21:29:41 -04:00
ceph Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client 2012-03-28 10:01:29 -07:00
cifs Use correct conversion specifiers in cifs_show_options 2012-04-24 11:36:25 -05:00
coda Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
configfs make configfs_pin_fs() return root dentry on success 2012-03-20 21:29:48 -04:00
cramfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
debugfs simple_open: automatically convert to simple_open() 2012-04-05 15:25:50 -07:00
devpts Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
dlm dlm fixes for 3.4 2012-04-23 18:22:42 -07:00
ecryptfs ecryptfs: make register_filesystem() the last potential failure exit 2012-03-20 21:29:49 -04:00
efs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
exofs Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd 2012-03-28 20:04:27 -07:00
exportfs
ext2 migrate ext2_fs.h guts to fs/ext2/ext2.h 2012-03-31 16:03:16 -04:00
ext3 ext3: move headers to fs/ext3/ 2012-03-31 16:03:16 -04:00
ext4 Ext4 bug fixes for 3.4 2012-04-23 19:52:00 -07:00
fat fat: fix bug in enforcing Long File Name length 2012-03-23 16:58:40 -07:00
freevxfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
fscache
fuse Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse 2012-04-18 17:29:05 -07:00
gfs2 GFS2: Instruct DLM to avoid queue convert slowdown 2012-04-24 13:26:50 +01:00
hfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hfsplus hfsplus: add an ioctl to bless files 2012-03-20 21:29:53 -04:00
hostfs Merge branch 'for-linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml 2012-03-27 18:29:53 -07:00
hpfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hppfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hugetlbfs hugetlbfs: lockdep annotate root inode properly 2012-04-25 21:26:34 -07:00
isofs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
jbd Power management updates for 3.4 2012-03-21 10:15:51 -07:00
jbd2 jbd2: use GFP_NOFS for blkdev_issue_flush 2012-04-23 21:43:41 -04:00
jffs2 MTD merge for 3.4 2012-03-30 17:31:56 -07:00
jfs jfs: mising cleanup on register_filesystem() failure 2012-03-20 21:29:48 -04:00
lockd lockd: fix the endianness bug 2012-04-13 13:50:52 -04:00
logfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
minix Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
ncpfs Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
nfs NFSv4: Keep dropped state owners on the LRU list for a while 2012-04-21 13:01:00 -04:00
nfs_common
nfsd Merge branch 'for-3.4' of git://linux-nfs.org/~bfields/linux 2012-04-19 14:54:52 -07:00
nilfs2 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
nls NLS: raname "maxlen" to "maxout" in UTF conversion routines 2011-11-26 19:58:47 -08:00
notify fs/notify/notification.c: make subsys_initcall function static 2012-03-23 16:58:31 -07:00
ntfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
ocfs2 ocfs2: ->e_leaf_clusters endianness breakage 2012-04-13 12:31:43 -04:00
omfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
openpromfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
proc revert "proc: clear_refs: do not clear reserved pages" 2012-04-25 21:26:34 -07:00
pstore Merge branch 'akpm' (Andrew's patch-bomb) 2012-04-05 15:30:34 -07:00
qnx4 qnx4: new helper - try_extent() 2012-03-20 21:29:52 -04:00
qnx6 fs: initial qnx6fs addition 2012-03-20 21:29:38 -04:00
quota Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2012-03-28 10:00:14 -07:00
ramfs tidy up after d_make_root() conversion 2012-03-20 21:29:37 -04:00
reiserfs Disintegrate and delete asm/system.h 2012-03-28 15:58:21 -07:00
romfs MTD merge for 3.4 2012-03-30 17:31:56 -07:00
squashfs Add an extra mount time sanity check, plus some code cleanups and bug fixes. 2012-03-28 18:05:54 -07:00
sysfs sysfs: handle 'parent deleted before child added' 2012-04-10 14:48:51 -07:00
sysv switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
ubifs - Improve error messages 2012-03-23 09:27:40 -07:00
udf Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2012-03-28 10:00:14 -07:00
ufs Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
xfs Disintegrate and delete asm/system.h 2012-03-28 15:58:21 -07:00
aio.c kill mm argument of vm_munmap() 2012-04-21 01:58:20 -04:00
anon_inodes.c anon_inodes: move allocation of anon_inode into ->mount() 2012-03-20 21:29:45 -04:00
attr.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
bad_inode.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
binfmt_aout.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_elf_fdpic.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_elf.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_em86.c __register_binfmt() made void 2012-03-20 21:29:46 -04:00
binfmt_flat.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_misc.c magic.h: move some FS magic numbers into magic.h 2012-03-23 16:58:31 -07:00
binfmt_script.c __register_binfmt() made void 2012-03-20 21:29:46 -04:00
binfmt_som.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
bio-integrity.c fs: remove the second argument of k[un]map_atomic() 2012-03-20 21:48:21 +08:00
bio.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
block_dev.c magic.h: move some FS magic numbers into magic.h 2012-03-23 16:58:31 -07:00
buffer.c fs/buffer.c: remove BUG() in possible but rare condition 2012-04-25 21:26:33 -07:00
char_dev.c char_dev.c: fix up some whitespace errors 2011-12-13 11:18:17 -08:00
compat_binfmt_elf.c
compat_ioctl.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
compat.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
dcache.c vfs: fix d_ancestor() case in d_materialize_unique 2012-03-28 09:54:34 -07:00
dcookies.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
direct-io.c Restore direct_io / truncate locking API 2012-02-23 15:56:21 -08:00
drop_caches.c
eventfd.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
eventpoll.c epoll: clear the tfile_check_list on -ELOOP 2012-04-25 21:26:33 -07:00
exec.c Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-04-04 10:04:42 -07:00
fcntl.c Wrap accesses to the fd_sets in struct fdtable 2012-02-19 10:30:52 -08:00
fhandle.c vfs: prefer ->dentry->d_sb to ->mnt->mnt_sb 2012-01-06 23:16:53 -05:00
fifo.c
file_table.c vfs: drop_file_write_access() made static 2012-03-20 21:29:32 -04:00
file.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
filesystems.c vfs: convert fs_supers to hlist 2012-01-03 22:52:39 -05:00
fs_struct.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
fs-writeback.c trivial writeback fixes 2012-03-28 10:07:27 -07:00
generic_acl.c
inode.c trim includes in inode.c 2012-03-20 21:29:51 -04:00
internal.h vfs: protect remounting superblock read-only 2012-01-06 23:20:12 -05:00
ioctl.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
ioprio.c block: strip out locking optimization in put_io_context() 2012-02-07 07:51:30 +01:00
Kconfig Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
Kconfig.binfmt fs: binfmt_elf: create Kconfig variable for PIE randomization 2012-01-10 16:30:51 -08:00
libfs.c dentry leak in simple_fill_super() failure exit 2012-04-09 01:39:22 -04:00
locks.c CIFS: Fix VFS lock usage for oplocked files 2012-04-01 13:54:27 -05:00
Makefile fs: initial qnx6fs addition 2012-03-20 21:29:38 -04:00
mbcache.c
mount.h vfs: keep list of mounts for each superblock 2012-01-06 23:20:12 -05:00
mpage.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
namei.c Make the "word-at-a-time" helper functions more commonly usable 2012-04-06 13:54:56 -07:00
namespace.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2012-01-08 13:21:22 -08:00
no-block.c
open.c Wrap accesses to the fd_sets in struct fdtable 2012-02-19 10:30:52 -08:00
pipe.c pipes: add a "packetized pipe" mode for writing 2012-04-29 13:12:42 -07:00
pnode.c vfs: switch pnode.h macros to struct mount * 2012-01-03 22:57:11 -05:00
pnode.h vfs: switch pnode.h macros to struct mount * 2012-01-03 22:57:11 -05:00
posix_acl.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
proc_namespace.c vfs: switch ->show_options() to struct dentry * 2012-01-06 23:19:54 -05:00
read_write.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
read_write.h
readdir.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
select.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
seq_file.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
signalfd.c epoll: ep_unregister_pollwait() can use the freed pwq->whead 2012-02-24 11:42:50 -08:00
splice.c tcp: tcp_sendpages() should call tcp_push() once 2012-04-05 19:04:27 -04:00
stack.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
stat.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
statfs.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
super.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
sync.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
timerfd.c
utimes.c
xattr_acl.c fs: reduce the use of module.h wherever possible 2012-02-28 19:31:58 -05:00
xattr.c fs/xattr.c:setxattr(): improve handling of allocation failures 2012-04-05 15:25:50 -07:00