Re: BUG: fast-import, ftruncate, and file mode

[Elijah Newren <newren@gmail.com>]

On Wed, Feb 23, 2022 at 5:59 AM Phillip Wood <phillip.wood123@gmail.com> wrote:
>
> On 23/02/2022 07:47, Elijah Newren wrote:
> > Hi,
> >
> > fast-import makes use of odb_mkstemp(), which creates a secure
> > temporary file and opens it with mode 0444, and then uses it for its
> > packfile writing.  Sometimes, fast-import will call its
> > truncate_pack() function, which makes use of ftruncate().
> >
> > According to my local manpage, "With ftruncate(), the file must be
> > open for writing; with truncate(), the file must be writable."
> >
> > The writable requirement does not appear to be enforced by the kernel
> > on common filesystems like ext4 or zfs, but this is enforced on some
> > filesystems.  Apparently a "VxFS Veritas filesystem" got triggered by
> > this...and some helpful bug reporters tracked this problem down and
> > found a workaround (for the filter-repo usecase, they recompiled a
> > special copy of git using mode 0644 for odb_mkstemp, since it was just
> > an intermediate step anyway and won't be used elsewhere).
>
> Am I missing something or is this really a file system bug? Surely if we
> have opened a file for writing the file permissions when we call
> ftruncate() should be irrelevant?
>
> Best Wishes
>
> Phillip

Oh, indeed, looks like I can't read late at night.  Sorry for the noise.