bug: "fatal: cannot pread pack file", version 1.7.5.4

> Hi,
>
> I have used git for some time and regularly pushed changes to another
> server (as some kind of backup), but today I got this error during
> git push`:
>
> Counting objects: 1293, done.
> Compressing objects: 100% (1027/1027), done.
> Writing objects: 100% (1229/1229), 70.83 MiB | 364 KiB/s, done.
> Total 1229 (delta 343), reused 0 (delta 0)
> fatal: cannot pread pack file: No such file or directory

> I have used git for some time and regularly pushed changes to another
> server (as some kind of backup), but today I got this error during
> `git push`:
> 
> Counting objects: 1293, done.
> Compressing objects: 100% (1027/1027), done.
> Writing objects: 100% (1229/1229), 70.83 MiB | 364 KiB/s, done.
> Total 1229 (delta 343), reused 0 (delta 0)
> fatal: cannot pread pack file: No such file or directory
> error: unpack failed: index-pack abnormal exit
> To user@host:~/path/
> ! [remote rejected] master -> master (n/a (unpacker error))
> error: failed to push some refs to 'user@host:~/path/'
> 
> I found similar bug reports suggesting to upgrade too version 1.7.x,
> but I am already using git version 1.7.5.4. Can somebody explain to
> me what this error is about? What can I do to resolve it / is there a
> workaround?

> Jeff King <peff@peff.net> writes:
>
>> It's very odd for pread to report ENOENT (since it is always operating
>> on an already-opened file descriptor).
>
> It doesn't, but gettext will clobber errno:
>
> 		n = pread(pack_fd, inbuf, n, from);
> 		if (n < 0)
> 			die_errno(_("cannot pread pack file"));
>
> There is nothing that saves errno.  This isn't limited to i18n though,
> any function call in the arguments may potentially clobber errno.

> Jeff King <peff@peff.net> writes:
> 
> > It's very odd for pread to report ENOENT (since it is always operating
> > on an already-opened file descriptor).
> 
> It doesn't, but gettext will clobber errno:
> 
> 		n = pread(pack_fd, inbuf, n, from);
> 		if (n < 0)
> 			die_errno(_("cannot pread pack file"));
> 
> There is nothing that saves errno.  This isn't limited to i18n though,
> any function call in the arguments may potentially clobber errno.

> On Tue, Jul 03, 2012 at 12:43:42AM +0200, Andreas Schwab wrote:
>
>> Jeff King <peff@peff.net> writes:
>>
>> > It's very odd for pread to report ENOENT (since it is always operating
>> > on an already-opened file descriptor).
>>
>> It doesn't, but gettext will clobber errno:
>>
>>               n = pread(pack_fd, inbuf, n, from);
>>               if (n < 0)
>>                       die_errno(_("cannot pread pack file"));
>>
>> There is nothing that saves errno.  This isn't limited to i18n though,
>> any function call in the arguments may potentially clobber errno.
>
> That's horribly lame of gettext. I don't expect arbitrary functions to
> save errno, but when the entire purpose of a function is to be a
> non-intrusive wrapper to massage messages to the user, it seems kind of
> evil to overwrite errno. Isn't the whole point of calling it "_" that
> you don't want to or have to notice it?

> Can we do something like this to get around it?
>
> diff --git a/gettext.h b/gettext.h
> index 57ba8bb..b7c3ae5 100644
> --- a/gettext.h
> +++ b/gettext.h
> @@ -44,7 +44,10 @@ extern int use_gettext_poison(void);
>
>  static inline FORMAT_PRESERVING(1) const char *_(const char *msgid)
>  {
> -       return use_gettext_poison() ? "# GETTEXT POISON #" : gettext(msgid);
> +       int saved_errno = errno;
> +       const char *r = use_gettext_poison() ? "# GETTEXT POISON #" : gettext(msgid);
> +       errno = saved_errno;
> +       return r;
>  }
>
>  static inline FORMAT_PRESERVING(1) FORMAT_PRESERVING(2)

> On Tue, Jul 3, 2012 at 10:45 AM, Jeff King <peff@peff.net> wrote:
> > On Tue, Jul 03, 2012 at 12:43:42AM +0200, Andreas Schwab wrote:
> >
> >> Jeff King <peff@peff.net> writes:
> >>
> >> > It's very odd for pread to report ENOENT (since it is always operating
> >> > on an already-opened file descriptor).
> >>
> >> It doesn't, but gettext will clobber errno:
> >>
> >>               n = pread(pack_fd, inbuf, n, from);
> >>               if (n < 0)
> >>                       die_errno(_("cannot pread pack file"));
> >>
> >> There is nothing that saves errno.  This isn't limited to i18n though,
> >> any function call in the arguments may potentially clobber errno.
> >
> > That's horribly lame of gettext. I don't expect arbitrary functions to
> > save errno, but when the entire purpose of a function is to be a
> > non-intrusive wrapper to massage messages to the user, it seems kind of
> > evil to overwrite errno. Isn't the whole point of calling it "_" that
> > you don't want to or have to notice it?
> 
> Agreed.

> Hmm. According to gettext(3):
>
>   ERRORS
>          errno is not modified.
>
> And googling for "gettext" and "errno" reveals several bugfixes in GNU
> gettext to make sure that gettext preserves errno. I wonder if there are
> systems where that is not the case, though; I don't know what non-GNU
> gettext implementations are in common use these days. I'd still be
> curious to hear what platform the server is for this bug report.

> On Tue, Jul 03, 2012 at 11:25:16AM +0700, Nguyen Thai Ngoc Duy wrote:
>
>> On Tue, Jul 3, 2012 at 10:45 AM, Jeff King <peff@peff.net> wrote:
>> > On Tue, Jul 03, 2012 at 12:43:42AM +0200, Andreas Schwab wrote:
>> >
>> >> Jeff King <peff@peff.net> writes:
>> >>
>> >> > It's very odd for pread to report ENOENT (since it is always operating
>> >> > on an already-opened file descriptor).
>> >>
>> >> It doesn't, but gettext will clobber errno:
>> >>
>> >>               n = pread(pack_fd, inbuf, n, from);
>> >>               if (n < 0)
>> >>                       die_errno(_("cannot pread pack file"));
>> >>
>> >> There is nothing that saves errno.  This isn't limited to i18n though,
>> >> any function call in the arguments may potentially clobber errno.
>> >
>> > That's horribly lame of gettext. I don't expect arbitrary functions to
>> > save errno, but when the entire purpose of a function is to be a
>> > non-intrusive wrapper to massage messages to the user, it seems kind of
>> > evil to overwrite errno. Isn't the whole point of calling it "_" that
>> > you don't want to or have to notice it?
>> 
>> Agreed.
>
> Hmm. According to gettext(3):
>
>   ERRORS
>          errno is not modified.
>
> And googling for "gettext" and "errno" reveals several bugfixes in GNU
> gettext to make sure that gettext preserves errno. I wonder if there are
> systems where that is not the case, though; I don't know what non-GNU
> gettext implementations are in common use these days. I'd still be
> curious to hear what platform the server is for this bug report.

> Jeff King <peff@peff.net> writes:
> 
>> On Tue, Jul 03, 2012 at 11:25:16AM +0700, Nguyen Thai Ngoc Duy wrote:
>>
>>> On Tue, Jul 3, 2012 at 10:45 AM, Jeff King <peff@peff.net> wrote:
>>> > On Tue, Jul 03, 2012 at 12:43:42AM +0200, Andreas Schwab wrote:
>>> >
>>> >> Jeff King <peff@peff.net> writes:
>>> >>
>>> >> > It's very odd for pread to report ENOENT (since it is always operating
>>> >> > on an already-opened file descriptor).
>>> >>
>>> >> It doesn't, but gettext will clobber errno:
>>> >>
>>> >>               n = pread(pack_fd, inbuf, n, from);
>>> >>               if (n < 0)
>>> >>                       die_errno(_("cannot pread pack file"));
>>> >>
>>> >> There is nothing that saves errno.  This isn't limited to i18n though,
>>> >> any function call in the arguments may potentially clobber errno.
>>> >
>>> > That's horribly lame of gettext. I don't expect arbitrary functions to
>>> > save errno, but when the entire purpose of a function is to be a
>>> > non-intrusive wrapper to massage messages to the user, it seems kind of
>>> > evil to overwrite errno. Isn't the whole point of calling it "_" that
>>> > you don't want to or have to notice it?
>>>
>>> Agreed.
>>
>> Hmm. According to gettext(3):
>>
>>   ERRORS
>>          errno is not modified.
>>
>> And googling for "gettext" and "errno" reveals several bugfixes in GNU
>> gettext to make sure that gettext preserves errno. I wonder if there are
>> systems where that is not the case, though; I don't know what non-GNU
>> gettext implementations are in common use these days. I'd still be
>> curious to hear what platform the server is for this bug report.
> 
> Hrm, has this ever been resolved?

>> Hrm, has this ever been resolved?
>
> Thank you for asking.
> My local git version is 1.7.5.4, the server version that I actually
> ended up pushing the files to was however still some 1.6.x.
> So it was a false alarm. Sorry about that.

> Lars Winterfeld <lars.winterfeld@tu-ilmenau.de> writes:
> 
>>> Hrm, has this ever been resolved?
>>
>> Thank you for asking.
>> My local git version is 1.7.5.4, the server version that I actually
>> ended up pushing the files to was however still some 1.6.x.
>> So it was a false alarm. Sorry about that.
> 
> Not really.  Pushing or fetching by a new version of Git against old
> version of Git *should* work; otherwise it is a bug.

> Lars Winterfeld <lars.winterfeld@tu-ilmenau.de> writes:
> 
> >> Hrm, has this ever been resolved?
> >
> > Thank you for asking.
> > My local git version is 1.7.5.4, the server version that I actually
> > ended up pushing the files to was however still some 1.6.x.
> > So it was a false alarm. Sorry about that.
> 
> Not really.  Pushing or fetching by a new version of Git against old
> version of Git *should* work; otherwise it is a bug.

> On Thu, Aug 16, 2012 at 04:05:22PM -0700, Junio C Hamano wrote:
>
>> Lars Winterfeld <lars.winterfeld@tu-ilmenau.de> writes:
>> 
>> >> Hrm, has this ever been resolved?
>> >
>> > Thank you for asking.
>> > My local git version is 1.7.5.4, the server version that I actually
>> > ended up pushing the files to was however still some 1.6.x.
>> > So it was a false alarm. Sorry about that.
>> 
>> Not really.  Pushing or fetching by a new version of Git against old
>> version of Git *should* work; otherwise it is a bug.
>
> Yes, but there may be old bugs in the server version that have since
> been fixed. For example, the bug fixed by 838cd346 might be the cause of
> this (that fix went into 1.6.0.3).