Re: [PATCH v3] packed_ref_cache: don't use mmap() for small files

> Take a hint from commit ea68b0ce9f8 (hash-object: don't use mmap() for
> small files, 2010-02-21) and use read() instead of mmap() for small
> packed-refs files.
> 
> This also fixes the problem[1] where xmmap() returns NULL for zero
> length[2], for which munmap() later fails.
> 
> Alternatively, we could simply check for NULL before munmap(), or
> introduce xmunmap() that could be used together with xmmap(). However,
> always setting snapshot->buf to a valid pointer, by relying on
> xmalloc(0)'s fallback to 1-byte allocation, makes using snapshots
> easier.
> 
> [1] https://github.com/git-for-windows/git/issues/1410
> [2] Logic introduced in commit 9130ac1e196 (Better error messages for
>     corrupt databases, 2007-01-11)
> 
> Signed-off-by: Kim Gybels <kgybels@infogroep.be>
> ---
> 
> Change since v2: removed separate case for zero length as suggested by Peff,
> ensuring that snapshot->buf is always a valid pointer.