On Thu, Jul 2, 2015 at 11:31 AM, Renato Botelho <ga...@freebsd.org> wrote:
> Author: garga (ports committer)
> Date: Thu Jul  2 17:30:59 2015
> New Revision: 285050
> URL: https://svnweb.freebsd.org/changeset/base/285050
>
> Log:
>   When passwd or group information is changed (by pw, vipw, chpass, ...)
>   temporary file is created and then a rename() call move it to official file.
>   This operation didn't have any check to make sure data was written to disk
>   and if a power cycle happens system could end up with a 0 length passwd
>   or group database.
>
>   There is a pfSense bug with more infor about it:
>
>   https://redmine.pfsense.org/issues/4523
>
>   The following changes were made to protect passwd and group operations:
>
>   * lib/libutil/gr_util.c:
>    - Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file
>    - After rename(), fsync() call on directory for faster result
>
>   * lib/libutil/pw_util.c
>    - Replace mkstemp() by mkostemp() with O_SYNC flag to create temp file
>
>   * usr.sbin/pwd_mkdb/pwd_mkdb.c
>    - Added O_SYNC flag on dbopen() calls
>    - After rename(), fsync() call on directory for faster result
>
>   * lib/libutil/pw_util.3
>    - pw_lock() returns a file descriptor to master password file on success
>
>   Differential Revision:        https://reviews.freebsd.org/D2978
>   Approved by:  bapt
>   Sponsored by: Netgate
>
> Modified:
>   head/lib/libutil/gr_util.c
>   head/lib/libutil/pw_util.3
>   head/lib/libutil/pw_util.c
>   head/usr.sbin/pwd_mkdb/pwd_mkdb.c

This change is making certain pw operations very slow on ZFS root
systems.  The problem is that when you open a file with O_SYNC, every
single write(2) call turns into a zil_commit on ZFS, which is fairly
expensive.  Did you consider using fsync(2) on the temporary files
instead of opening them with O_SYNC?  I just tried that now, and I see
a considerable speedup when running the tests in
/usr/tests/usr.sbin/pw:

Using O_SYNC, as CURRENT does: 4 minutes 5.2 seconds
No synchronous operations at all: 49.5 seconds
Using fsync(2): 56.0 seconds

-Alan
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