Re: pread() over NFS (again) [1.5.5.4]

[Christian Holtje <docwhat@gmail.com>]

On Jun 26, 2008, at 5:05 PM, Shawn O. Pearce wrote:
> Junio C Hamano <gitster@pobox.com> wrote:
>> "Shawn O. Pearce" <spearce@spearce.org> writes:
>>> Christian Holtje <docwhat@gmail.com> wrote:
>>>> I have read all the threads on git having trouble with pread()  
>>>> and I
>>>> didn't see anything to help.
>>> ...
>>>>  Receiving objects: 100% (253/253), 5.27 MiB | 9136 KiB/s, done.
>>>>  fatal: cannot pread pack file: No such file or directory
>>>>  fatal: index-pack failed
>>>>
>>>> The end of the strace looks like so:
>>>> pread(3, "", 205, 1373)                 = 0
>>>> write(2, "fatal: cannot pread pack file: N"..., 57) = 57
>>>
>>> Hmmph.  So pread for a length of 205 can return 0 on NFS?  Is this
>>> a transient error?  If so, perhaps a patch like this might help:
> ...
>>> The file shouldn't be short unless someone truncated it, or there
>>> is a bug in index-pack.  Neither is very likely, but I don't think
>>> we would want to retry pread'ing the same block forever.
>>
>> I don't think we would want to retry even once.  Return value of 0  
>> from
>> pread is defined to be an EOF, isn't it?
>
> Indeed, it is defined to be EOF, but EOF here makes no sense.
>
> We have a file position we saw once before as the start of a delta.
> We wrote it down to disk.  We want to go back and open it up, as
> we have the base decompressed and in memory and need to compute
> the SHA-1 of the object that resides at this offset.
>
> And *wham* we get an EOF.  Where there should be data.  Where we
> know there is data.
>
> I'm open to the idea that index-pack has a bug, but I doubt it.
> We shovel hundreds of megabytes through that on a daily basis
> across all of the git users, and nobody ever sees it crash out
> with an EOF in the middle of an object it knows to be present.
> Except poor Christian on NFS.
>
> Actually, I think the last time someone reported something like this
> in Git it turned out to be an NFS kernel bug.  I didn't quote it
> in my reply to him, but I think he did say this was a linux client,
> linux server.

I did see the threads that talked about NFS, but I couldn't find any  
matching messages in the linux kernel mailing list.  If someone can  
give me a pointer to where this picked up on other mailing lists (say,  
via a URL) then I'll take that back to IT as a reason to upgrade.

Would it be a bug in the client or server?  I'd assume client...

The other NFS/pread() email thread was also a client of linux 2.6.9....

Ciao!