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  1. 05 Nov, 2002 3 commits
    • Andrew Morton's avatar
      [PATCH] `event' removal: other filesystems · 9448b90c
      Andrew Morton authored 
      Patch from Manfred Spraul

Several filesystems compare f_version and i_version to validate
directory positions in readdir(): The directory position is revalidated
if i_version is not equal f_version.  Operations that could invalidate
the cached position set i_version or f_version to '++event', event is a
global variable.  Global uniqueness is not needed, 'i_version++' and
'f_version=0' is sufficient to guarantee that the next readdir() will
revalidate the directory position, and that avoids the need for an ugly
global variable.

The attached patch converts all filesystems except ext2, which was
converted with a seperate patch.
      9448b90c
    • Andrew Morton's avatar
      [PATCH] `event' removal: ext2 · 9aefc010
      Andrew Morton authored 
      Patch from Manfred Spraul

Use a local counter instead of the global 'event' variable for the
readdir() optimization.

Depends on patch-event-II

Background:
  The only user of i_version and f_version in ext2 is
  ext2_readdir(). As an optimization, ext2 performs the
  validation of the start position for readdir() only if
        flip->f_version != inode->i_version.
  If there was no llseek and no directory change since the
  last readdir() call, then f_pos can be trusted.
  f_version is set to 0 in get_empty_flip and during llseek.
  Right now, i_version set to ++event during ext2_read_inode
  and commit_chunk, i.e. at inode creation and if a directory
  is changed.
  Initializing i_version to 1, and updating with i_version++
  achieves the same effect, without the need of a global variable.
  Global uniqueness is not required, there are no other uses
  of [if]_version in ext2.

Change relative to the patch you have right now:
i_version is initialized to 1 instead of 0. For ext2 it's doesn't
matter [there is always a valid 'len' value at the beginning of a
directory data block], but it's cleaner.
      9aefc010
    • Andrew Morton's avatar
      [PATCH] `event' removal: core kernel · 4ccf7a32
      Andrew Morton authored 
      Patch from Manfred Spraul

f_version and i_version are used by filesystems to check if it can
reuse the f_pos position across readdir calls without validation.

Right now f_version and i_version are modified by
    f_version = ++event;
    i_version = ++event;
    if (f_version != i_version) goto revalidate
and event is a global, exported variable.

But that's not needed,
    f_version  = 0;
    i_version++;
    if (f_version != i_version) goto revalidate
works too, without the ugly 'event' variable.

I got an ok from viro, and I had notified the fs maintainers, no
complaints either

- block_dev.c, block_llseek updates f_version to '++event'.
   grep showed that no device driver uses f_version, this is dead
   code copied from the default llseek implementation.

- the llseek implementations and get_empty_flip set f_version
   to '++event'
   This is not dead code, but
            filp->f_version = 0
   achieves the same effect:
   f_version is used by the readdir() implementation of several
   filesystems to skip the revalidation of f_pos at the beginning
   of a readdir call: If llseek was not called and the filesystem
   did not change since the last readdir call, then the value in
   f_pos can be trusted.
   The implementation (for example in ext2) is
     inode->i_version = ++event;
   in all operations that change a directory
   At the beginning of file_operation->readdir():
     if(inode->i_version != flip->f_version)
                revalidate();
     filp->f_version = inode->i_version;
   There are other users of f_version, but none of them use the
   default llseek implementation (e.g. fs/pipe.c)
      4ccf7a32
  3. 04 Nov, 2002 7 commits
  5. 03 Nov, 2002 30 commits
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