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NeilBrown 1f4aace60b fs/seq_file.c: simplify seq_file iteration code and interface 
The documentation for seq_file suggests that it is necessary to be able
to move the iterator to a given offset, however that is not the case.
If the iterator is stored in the private data and is stable from one
read() syscall to the next, it is only necessary to support first/next
interactions.  Implementing this in a client is a little clumsy.

 - if ->start() is given a pos of zero, it should go to start of
   sequence.

 - if ->start() is given the name pos that was given to the most recent
   next() or start(), it should restore the iterator to state just
   before that last call

 - if ->start is given another number, it should set the iterator one
   beyond the start just before the last ->start or ->next call.

Also, the documentation says that the implementation can interpret the
pos however it likes (other than zero meaning start), but seq_file
increments the pos sometimes which does impose on the implementation.

This patch simplifies the interface for first/next iteration and
simplifies the code, while maintaining complete backward compatability.
Now:

 - if ->start() is given a pos of zero, it should return an iterator
   placed at the start of the sequence

 - if ->start() is given a non-zero pos, it should return the iterator
   in the same state it was after the last ->start or ->next.

This is particularly useful for interators which walk the multiple
chains in a hash table, e.g.  using rhashtable_walk*.  See
fs/gfs2/glock.c and drivers/staging/lustre/lustre/llite/vvp_dev.c

A large part of achieving this is to *always* call ->next after ->show
has successfully stored all of an entry in the buffer.  Never just
increment the index instead.  Also:

 - always pass &m->index to ->start() and ->next(), never a temp
   variable

 - don't clear ->from when ->count is zero, as ->from is dead when
   ->count is zero.

Some ->next functions do not increment *pos when they return NULL.  To
maintain compatability with this, we still need to increment m->index in
one place, if ->next didn't increment it.  Note that such ->next
functions are buggy and should be fixed.  A simple demonstration is

   dd if=/proc/swaps bs=1000 skip=1

Choose any block size larger than the size of /proc/swaps.  This will
always show the whole last line of /proc/swaps.

This patch doesn't work around buggy next() functions for this case.

[neilb@suse.com: ensure ->from is valid]
  Link: http://lkml.kernel.org/r/87601ryb8a.fsf@notabene.neil.brown.name
Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>	[docs]
Tested-by: Jann Horn <jannh@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2018-08-17 16:20:28 -07:00
..
9p get rid of 'opened' argument of ->atomic_open() - part 3 2018-07-12 10:04:20 -04:00
adfs adfs: don't put inodes into icache 2018-08-03 16:03:33 -04:00
affs affs: fix potential memory leak when parsing option 'prefix' 2018-05-28 12:36:41 +02:00
afs Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2018-08-15 15:04:25 -07:00
autofs autofs: fix slab out of bounds read in getname_kernel() 2018-07-14 11:11:09 -07:00
befs fix a series of Documentation/ broken file name references 2018-06-15 18:10:01 -03:00
bfs bfs_add_entry: pass name/len as qstr pointer 2018-05-22 14:27:50 -04:00
btrfs for-4.19-tag 2018-08-13 21:58:53 -07:00
cachefiles cachefiles: Wait rather than BUG'ing on "Unexpected object collision" 2018-07-25 14:49:00 +01:00
ceph Merge branch 'work.open3' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 19:58:36 -07:00
cifs smb3/cifs fixes (including 8 for stable). Improved tracing, stats, snapshots (previous version mounts work now), performance (compounding enabled for statfs) 2018-08-13 22:32:11 -07:00
coda vfs: change inode times to use struct timespec64 2018-06-05 16:57:31 -07:00
configfs configfs: fix registered group removal 2018-07-17 06:14:07 -07:00
cramfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
crypto f2fs-for-4.18-rc1 2018-06-11 10:16:13 -07:00
debugfs Revert "debugfs: inode: debugfs_create_dir uses mode permission from parent" 2018-06-12 20:52:16 -07:00
devpts devpts: comment devpts_mntget() 2018-03-14 13:31:23 +01:00
dlm treewide: Use array_size() in vmalloc() 2018-06-12 16:19:22 -07:00
ecryptfs Merge branch 'fixes' of https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs into aio-base 2018-05-26 09:16:25 +02:00
efivarfs efivars: Call guid_parse() against guid_t type of variable 2018-07-22 14:13:44 +02:00
efs
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exofs exofs: use bio_clone_fast in _write_mirror 2018-07-24 14:43:20 -06:00
exportfs ovl: do not try to reconnect a disconnected origin dentry 2018-04-12 12:04:49 +02:00
ext2 dax: remove VM_MIXEDMAP for fsdax and device dax 2018-08-17 16:20:27 -07:00
ext4 dax: remove VM_MIXEDMAP for fsdax and device dax 2018-08-17 16:20:27 -07:00
f2fs block: Define and use STAT_READ and STAT_WRITE 2018-07-18 08:44:18 -06:00
fat fat: fix memory allocation failure handling of match_strdup() 2018-07-21 12:50:46 -07:00
freevxfs freevxfs_lookup(): use d_splice_alias() 2018-05-22 14:27:51 -04:00
fscache fscache: Fix reference overput in fscache_attach_object() error handling 2018-07-25 14:49:00 +01:00
fuse Merge branch 'work.mkdir' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:25:58 -07:00
gfs2 gfs2 4.19 merge 2018-08-15 22:40:03 -07:00
hfs new helper: inode_fake_hash() 2018-08-03 16:03:32 -04:00
hfsplus vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
hostfs vfs: discard ATTR_ATTR_FLAG 2018-08-17 16:20:28 -07:00
hpfs fs/hpfs: extend gmt_to_local() conversion to 64-bit times 2018-08-17 16:20:27 -07:00
hugetlbfs Merge branch 'work.open3' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 19:58:36 -07:00
isofs isofs: fix potential memory leak in mount option parsing 2018-04-16 09:47:41 +02:00
jbd2 jbd2: replace current_kernel_time64 with ktime equivalent 2018-07-29 15:51:47 -04:00
jffs2 jffs2: use unsigned 32-bit timstamps consistently 2018-07-18 16:44:01 +02:00
jfs Just one jfs patch for 4.19 2018-08-15 22:47:23 -07:00
kernfs kernfs: allow creating kernfs objects with arbitrary uid/gid 2018-07-20 23:44:35 -07:00
lockd net: Drop pernet_operations::async 2018-03-27 13:18:09 -04:00
minix minix_lookup: use d_splice_alias() 2018-05-22 14:27:52 -04:00
nfs Merge branch 'work.mkdir' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:25:58 -07:00
nfs_common net: Drop pernet_operations::async 2018-03-27 13:18:09 -04:00
nfsd IMA: don't propagate opened through the entire thing 2018-07-12 10:04:19 -04:00
nilfs2 do d_instantiate/unlock_new_inode combinations safely 2018-05-11 15:36:37 -04:00
nls
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notify fsnotify: add fsnotify_add_inode_mark() wrappers 2018-05-18 14:58:22 +02:00
ntfs ntfs: mft: remove VLA usage 2018-08-17 16:20:27 -07:00
ocfs2 ocfs2: make several functions and variables static (and some const) 2018-08-17 16:20:28 -07:00
omfs omfs_lookup(): report IO errors, use d_splice_alias() 2018-05-22 14:27:58 -04:00
openpromfs openpromfs: switch to d_splice_alias() 2018-05-22 14:27:57 -04:00
orangefs orangefs: remove redundant pointer orangefs_inode 2018-08-14 12:07:14 -04:00
overlayfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
proc fs/proc/task_mmu.c: fix Locked field in /proc/pid/smaps* 2018-07-14 11:11:09 -07:00
pstore pstore: add zstd compression support 2018-08-03 18:12:18 -07:00
qnx4 qnx4_lookup: use d_splice_alias() 2018-05-22 14:27:52 -04:00
qnx6 qnx6_lookup: switch to d_splice_alias() 2018-05-22 14:27:54 -04:00
quota quota: Cleanup list iteration in dqcache_shrink_scan() 2018-06-20 11:04:26 +02:00
ramfs
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reiserfs reiserfs: fix buffer overflow with long warning messages 2018-07-14 11:11:10 -07:00
romfs romfs_lookup: switch to d_splice_alias() 2018-05-22 14:27:55 -04:00
squashfs Squashfs: Compute expected length from inode size rather than block length 2018-08-02 09:34:02 -07:00
sysfs SCSI misc on 20180815 2018-08-15 22:06:26 -07:00
sysv sysv_lookup: use d_splice_alias() 2018-05-22 14:27:53 -04:00
tracefs
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ubifs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
udf Merge branch 'work.mkdir' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:25:58 -07:00
ufs fs/ufs: use ktime_get_real_seconds for sb and cg timestamps 2018-08-17 16:20:27 -07:00
xfs dax: remove VM_MIXEDMAP for fsdax and device dax 2018-08-17 16:20:27 -07:00
Kconfig autofs: remove left-over autofs4 stubs 2018-06-11 08:22:34 -07:00
Kconfig.binfmt kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
Makefile autofs: remove left-over autofs4 stubs 2018-06-11 08:22:34 -07:00
aio.c Merge branch 'work.aio' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:56:23 -07:00
anon_inodes.c anon_inode_getfile(): switch to alloc_file_pseudo() 2018-07-12 10:04:27 -04:00
attr.c fs: Fix attr.c kernel-doc 2018-07-03 16:44:45 -04:00
bad_inode.c get rid of 'opened' argument of ->atomic_open() - part 3 2018-07-12 10:04:20 -04:00
binfmt_aout.c exec: introduce finalize_exec() before start_thread() 2018-04-11 10:28:37 -07:00
binfmt_elf.c Here are the main MIPS changes for 4.19. 2018-08-13 19:24:32 -07:00
binfmt_elf_fdpic.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
binfmt_em86.c
…
binfmt_flat.c exec: introduce finalize_exec() before start_thread() 2018-04-11 10:28:37 -07:00
binfmt_misc.c turn filp_clone_open() into inline wrapper for dentry_open() 2018-07-10 23:29:03 -04:00
binfmt_script.c
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block_dev.c for-4.19/block-20180812 2018-08-14 10:23:25 -07:00
buffer.c iomap: mark newly allocated buffer heads as new 2018-06-19 15:10:55 -07:00
char_dev.c block, char_dev: Use correct format specifier for unsigned ints 2018-03-15 17:59:24 +01:00
compat.c ncpfs: remove compat functionality 2018-06-05 19:23:26 +02:00
compat_binfmt_elf.c
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compat_ioctl.c media: dvb/audio.h: get rid of unused APIs 2018-07-30 16:21:49 -04:00
coredump.c
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d_path.c split d_path() and friends into a separate file 2018-03-29 15:07:46 -04:00
dax.c dax: dax_layout_busy_page() warn on !exceptional 2018-07-29 16:59:16 -04:00
dcache.c fs/dcache.c: fix kmemcheck splat at take_dentry_name_snapshot() 2018-08-17 16:20:28 -07:00
dcookies.c fs: add do_lookup_dcookie() helper; remove in-kernel call to syscall 2018-04-02 20:15:39 +02:00
direct-io.c block: consistently use GFP_NOIO instead of __GFP_NORECLAIM 2018-05-14 08:55:18 -06:00
drop_caches.c
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eventfd.c Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL 2018-06-28 10:40:47 -07:00
eventpoll.c Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL 2018-06-28 10:40:47 -07:00
exec.c mm: fix vma_is_anonymous() false-positives 2018-07-26 19:38:03 -07:00
fcntl.c mm: restructure memfd code 2018-06-07 17:34:35 -07:00
fhandle.c
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file.c fs: add ksys_close() wrapper; remove in-kernel calls to sys_close() 2018-04-02 20:16:00 +02:00
file_table.c make alloc_file() static 2018-07-12 10:04:29 -04:00
filesystems.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
fs-writeback.c bdi: Fix oops in wb_workfn() 2018-05-03 16:11:37 -06:00
fs_pin.c
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fs_struct.c
…
inode.c Merge branch 'work.mkdir' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:25:58 -07:00
internal.h Merge branch 'iomap-4.19-merge' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux 2018-08-13 22:29:03 -07:00
ioctl.c fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems 2018-05-24 12:04:28 -05:00
iomap.c Changes for 4.19: 2018-08-14 08:56:02 -07:00
libfs.c fs, dax: prepare for dax-specific address_space_operations 2018-03-30 11:34:55 -07:00
locks.c File locking fixes and enhancements for v4.19 2018-08-13 21:56:50 -07:00
mbcache.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
mount.h
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mpage.c block: make bdev_ops->rw_page() take a REQ_OP instead of bool 2018-07-18 08:44:14 -06:00
namei.c Merge branches 'work.misc' and 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 21:28:25 -07:00
namespace.c fix __legitimize_mnt()/mntput() race 2018-08-09 17:51:32 -04:00
no-block.c
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nsfs.c net: Export open_related_ns() 2018-02-15 15:34:42 -05:00
open.c ->atomic_open(): return 0 in all success cases 2018-07-12 10:04:21 -04:00
pipe.c Merge branch 'work.open3' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 19:58:36 -07:00
pnode.c
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pnode.h
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posix_acl.c
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proc_namespace.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
read_write.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
readdir.c fs: add ksys_getdents64() helper; remove in-kernel calls to sys_getdents64() 2018-04-02 20:16:02 +02:00
select.c Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL 2018-06-28 10:40:47 -07:00
seq_file.c fs/seq_file.c: simplify seq_file iteration code and interface 2018-08-17 16:20:28 -07:00
signalfd.c Merge branch 'work.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:21:50 +09:00
splice.c Merge branch 'work.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:21:50 +09:00
stack.c
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stat.c fs: add do_readlinkat() helper; remove internal call to sys_readlinkat() 2018-04-02 20:15:34 +02:00
statfs.c kernel: add kcompat_sys_{f,}statfs64() 2018-07-12 14:49:48 +01:00
super.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-04 10:14:28 -07:00
sync.c Changes for this release: 2018-04-04 12:44:02 -07:00
timerfd.c Merge branch 'work.aio' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-08-13 20:56:23 -07:00
userfaultfd.c userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails 2018-08-02 16:03:40 -07:00
utimes.c fs: add do_compat_futimesat() helper; remove in-kernel call to compat syscall 2018-04-02 20:15:44 +02:00
xattr.c vfs: delete unnecessary assignment in vfs_listxattr 2018-05-29 13:22:41 -04:00