Am 07.05.22 um 14:33 schrieb Philip Oakley:
>
>
> On 7 May 2022 03:15:00 BST, Jason Hatton <jhatton@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Philip Oakley <philipoakley@iee.email> writes:
>
> This may treat non-zero multiple of 4GiB as "not racy", but has
> anybody double checked the concern Réne brought up earlier that a
> 4GiB file that was added and then got rewritten to 2GiB within the
> same second would suddenly start getting treated as not racy?
>
> This is the pre-existing problem, that ~1in 2^31 size changes might not
> get noticed for size change. The 0 byte / 4GiB change is an identical
> issue, as is changing from 3 bytes to 4GiB+3 bytes, etc., so that's no
> worse than before (well maybe twice as 'unlikely').
>
>
> OK, it added one more case to 2^32-1 existing cases, I guess.
>
> The patch (the firnal version of it anyway) needs to be accompanied
> by a handful of test additions to tickle corner cases like that.
>
> They'd be protected by the EXPENSIVE prerequisite I would assume.
>
>
> Oh, absolutely. Thanks for spelling that out.
>
>
> I have been testing out the patch a bit and have good and (mostly) bad news.
>
> What works using a munge value of 1.
>
> $ git add
> $ git status
>
> Racy seems to work.
>
> $ touch .git/index 4GiB # 4GiB is now racy
> $ git status # Git will rehash the racy file
> $ git status # Git cached the file. Second status is fast.
>
> What doesn't work.
>
> $ git checkout 4GiB
> $ fatal: packed object is corrupt!
>
> Using a munge value of 1<<31 causes even more problems. The file hash in the
> index for 4GiB files (git ls-files -s --debug) are set to the zero file hash.
>
> I looked up and down the code base and couldn't figure out how the munged
> value was leaking out of read-cache.c and breaking things. Most of the code
> I found tends to use stat and then convert that to a size_t, not using the
> munged unsigned int at all.
>
> Maybe someone else will have better luck. This seems over my head :(
>
> Thanks
> --
> Jason
>
>
> Is this on Git for Windows or a 64 bit Linux?
> There are still some issues on GfW for 2GiB+ files (long Vs long long int).
Which would explain the zero file hash. And make the platform unfit for
handling big files at all at this time.
FWIW, on MacOS I get this with the patch applied:
$ git init --quiet /tmp/a
$ cd /tmp/a
$ : >size-0
$ dd if=/dev/zero bs=1 oseek=4294967295 count=1 of=size-4294967296
1+0 records in
1+0 records out
1 bytes transferred in 0.000365 secs (2740 bytes/sec)
$ dd if=/dev/zero bs=1 oseek=4294967296 count=1 of=size-4294967297
1+0 records in
1+0 records out
1 bytes transferred in 0.000293 secs (3413 bytes/sec)
$ dd if=/dev/zero bs=1 oseek=6442450943 count=1 of=size-6442450944
1+0 records in
1+0 records out
1 bytes transferred in 0.000266 secs (3759 bytes/sec)
$ git add size-*
$ git commit -m initial
[master (root-commit) d9c2a0a] initial
4 files changed, 0 insertions(+), 0 deletions(-)
create mode 100644 size-0
create mode 100644 size-4294967296
create mode 100644 size-4294967297
create mode 100644 size-6442450944
$ time git checkout size-*
Updated 0 paths from the index
git checkout size-* 0.01s user 0.01s system 65% cpu 0.020 total
$ git ls-files -s --debug | grep size
100644 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 0 size-0
size: 0 flags: 0
100644 451971a31ea5a207a10b391df2d5949910133565 0 size-4294967296
size: 2147483648 flags: 0
100644 3eb7feb1413c757f0d8181deb28d1dab03d64846 0 size-4294967297
size: 1 flags: 0
100644 741285bddfa7863072c238f34e27144c2501832d 0 size-6442450944
size: 2147483648 flags: 0
So checkout skips all of the files and their cached sizes have the
expected values.
René
