John Baldwin wrote: > On Thursday, April 23, 2015 05:02:08 PM Julian Elischer wrote: > > On 4/23/15 11:20 AM, Julian Elischer wrote: > > > I'm debugging a problem being seen with samba 3.6. > > > > > > basically telldir/seekdir/readdir don't seem to work as > > > advertised.. > > > > ok so it looks like readdir() (and friends) is totally broken in > > the face > > of deletes unless you read the entire directory at once or reset to > > the > > the first file before the deletes, or earlier. > > I'm not sure that Samba isn't assuming non-portable behavior. For > example: > > From > http://pubs.opengroup.org/onlinepubs/009695399/functions/readdir_r.html > > If a file is removed from or added to the directory after the most > recent call > to opendir() or rewinddir(), whether a subsequent call to readdir() > returns an > entry for that file is unspecified. > > While this doesn't speak directly to your case, it does note that you > will > get inconsistencies if you scan a directory concurrent with add and > remove. > > UFS might kind of work actually since deletes do not compact the > backing > directory, but I suspect NFS and ZFS would not work. In addition, > our > current NFS support for seekdir is pretty flaky and can't be fixed > without > changes to return the seek offset for each directory entry (I believe > that > the projects/ino64 patches include this since they are breaking the > ABI of > the relevant structures already). The ABI breakage makes this a very > non-trivial task. However, even if you have that per-item cookie, it > is > likely meaningless in the face of filesystems that use any sort of > more > advanced structure than an array (such as trees, etc.) to store > directory > entries. POSIX specifically mentions this in the rationale for > seekdir: > > http://pubs.opengroup.org/onlinepubs/009695399/functions/seekdir.html > > One of the perceived problems of implementation is that returning to > a given point in a directory is quite difficult to describe > formally, in spite of its intuitive appeal, when systems that use > B-trees, hashing functions, or other similar mechanisms to order > their directories are considered. The definition of seekdir() and > telldir() does not specify whether, when using these interfaces, a > given directory entry will be seen at all, or more than once. > > In fact, given that quote, I would argue that what Samba is doing is > non-portable. This would seem to indicate that a conforming seekdir > could > just change readdir to immediately return EOF until you call > rewinddir. > Btw, Linux somehow makes readdir()/unlink() work for NFS. I haven't looked, but I strongly suspect that it reads the entire directory upon either opendir() or the first readdir().
Oh, and I hate to say it, but I suspect Linux defines the "standard" on this and not POSIX. (In other words, if it works on Linux, it isn't broken;-) rick > -- > John Baldwin > _______________________________________________ > email@example.com mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to > "freebsd-current-unsubscr...@freebsd.org" > _______________________________________________ firstname.lastname@example.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"