svn commit: r291936 - head/sys/ufs/ufs

[Bruce Evans]

On Mon, 7 Dec 2015, Andrey Chernov wrote:

> On 07.12.2015 17:42, Andrey Chernov wrote:
>> On 07.12.2015 15:09, Konstantin Belousov wrote:
>>> Author: kib
>>> Date: Mon Dec  7 12:09:04 2015
>>> New Revision: 291936
>>> URL: https://svnweb.freebsd.org/changeset/base/291936
>>>
>>> Log:
>>>   Update ctime when atime or birthtime are updated.
>>
>> Who calls ufs_itimes() and when to process IN_CHANGE flag in the new
>> version?

UFS_UPDATE() is called next and it call ufs_itimes().  Converting
IN_CHANGE from a mark to a time could be delayed safely, but the other
changes should be written soon.  We use a delayed write, so they are
not actually written very soon, and this could be optimized a little.
Setting IN_LAZYACCESS might work as a hack (just some flag that the
syncer checks and calls UFS_UPDATE() to clear).  Only do this for
unimportant attributes like times.  For ids, I would go the other
way and tell UFS_UPDATE() to do an async update.  It currently only
supports a waitfor boolean flag which selects bwrite() if set and
normally bdwrite() if clear unless under load when it selects
bawrite() if clear.

>>> -		ufs_itimes(vp);
>>> +		ip->i_flag |= IN_CHANGE | IN_MODIFIED;
>>
>
> New version also forces IN_MODIFIED flag old one tends to avoid (only
> for birthtime, and only for non-suspended systems in ufs_itimes()).

That was mostly obfuscation in the old version:
- for settings of the atime only, we modified the atime (possibly with
   a null change) but don't set IN_MODIFIED.  ufs_itimes() fixeed this
   up by translating IN_ACCESS to a modification of the atime and a
   setting of IN_MODIFIED.  This is depends on not being in the suspended
   case.  Then we overwrote the modification with the final one before
   writing
- for settings of the mtime only, ufs_itimes() fixes up IN_MODIFIED in
   the same way except this is obviously not affected by the suspended
   flag
- for settings of the birthtime only, ufs_itimes() had no effect unless
   some update marks were already set, so we had to set IN_MODIFIED
   directly.

The suspended case makes the side effects of ufs_itimes() even harder to
understand, except it doesn't actually occur for calls from VOP_SETATTR(),
since setattr is like write() -- it arranges for exclusive access and not
suspended.

Bruce