From: Jeff King <peff@peff.net>
To: Rohit Ashiwal via GitGitGadget <gitgitgadget@gmail.com>
Cc: Johannes Schindelin <johannes.schindelin@gmx.de>,
git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Subject: Re: [PATCH 1/2] archive: replace write_or_die() calls with write_block_or_die()
Date: Fri, 12 Apr 2019 21:34:52 -0400 [thread overview]
Message-ID: <20190413013451.GB2040@sigill.intra.peff.net> (raw)
In-Reply-To: <7a9525a78a7b7b237150b9264cf675a4a0b37267.1555110278.git.gitgitgadget@gmail.com>
On Fri, Apr 12, 2019 at 04:04:39PM -0700, Rohit Ashiwal via GitGitGadget wrote:
> From: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
>
> MinGit for Windows comes without `gzip` bundled inside, git-archive uses
> `gzip -cn` to compress tar files but for this to work, gzip needs to be
> present on the host system.
>
> In the next commit, we will change the gzip compression so that we no
> longer spawn `gzip` but let zlib perform the compression in the same
> process instead.
>
> In preparation for this, we consolidate all the block writes into a
> single function.
Sounds like a good preparatory step. This part confused me, though:
> @@ -38,11 +40,21 @@ static int write_tar_filter_archive(const struct archiver *ar,
> #define USTAR_MAX_MTIME 077777777777ULL
> #endif
>
> +/* writes out the whole block, or dies if fails */
> +static void write_block_or_die(const char *block) {
> + if (gzip) {
> + if (gzwrite(gzip, block, (unsigned) BLOCKSIZE) != BLOCKSIZE)
> + die(_("gzwrite failed"));
> + } else {
> + write_or_die(1, block, BLOCKSIZE);
> + }
> +}
What is gzwrite()? At first I thought this was an out-of-sequence bit of
the series, but it turns out that this is a zlib.h interface. So the
idea (I think) is that here we introduce a "gzip" variable that is
always false, and this first conditional arm is effectively dead code.
And then in a later patch we'd set up "gzip" and it would become
not-dead.
I think it would be less confusing if this just factored out
write_block_or_die(), which starts as a thin wrapper and then grows the
gzip parts in the next patch.
A few nits on the code itself:
> +static gzFile gzip;
> [...]
> + if (gzip) {
Is it OK for us to ask about the truthiness of this opaque type? That
works if it's really a pointer behind the scenes, but it seems like it
would be equally OK for zlib to declare it as a struct.
It looks OK in my version of zlib, and that library tends to be fairly
conservative so I wouldn't be surprised if it was that way back to the
beginning and remains that way for eternity. But it feels like a bad
pattern.
> + if (gzwrite(gzip, block, (unsigned) BLOCKSIZE) != BLOCKSIZE)
This cast is interesting. All of the matching write_or_die() calls are
promoting it to a size_t, which is also unsigned.
BLOCKSIZE is a constant. Should we be defining it with a "U" in the first place?
I doubt it matters much either way from a correctness perspective. I
just wonder when I see a cast like that if we're going to get unexpected
truncation or similar.
-Peff
next prev parent reply other threads:[~2019-04-13 1:34 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-12 23:04 [PATCH 0/2] Avoid spawning gzip in git archive Johannes Schindelin via GitGitGadget
2019-04-12 23:04 ` [PATCH 1/2] archive: replace write_or_die() calls with write_block_or_die() Rohit Ashiwal via GitGitGadget
2019-04-13 1:34 ` Jeff King [this message]
2019-04-13 5:51 ` Junio C Hamano
2019-04-14 4:36 ` Rohit Ashiwal
2019-04-26 14:29 ` Johannes Schindelin
2019-04-26 23:44 ` Junio C Hamano
2019-04-29 21:32 ` Johannes Schindelin
2019-05-01 18:09 ` Jeff King
2019-05-02 20:29 ` René Scharfe
2019-05-05 5:25 ` Junio C Hamano
2019-05-06 5:07 ` Jeff King
2019-04-14 4:34 ` Rohit Ashiwal
2019-04-14 10:33 ` Junio C Hamano
2019-04-26 14:28 ` Johannes Schindelin
2019-05-01 18:07 ` Jeff King
2019-04-12 23:04 ` [PATCH 2/2] archive: avoid spawning `gzip` Rohit Ashiwal via GitGitGadget
2019-04-13 1:51 ` Jeff King
2019-04-13 22:01 ` René Scharfe
2019-04-15 21:35 ` Jeff King
2019-04-26 14:51 ` Johannes Schindelin
2019-04-27 9:59 ` René Scharfe
2019-04-27 17:39 ` René Scharfe
2019-04-29 21:25 ` Johannes Schindelin
2019-05-01 17:45 ` René Scharfe
2019-05-01 18:18 ` Jeff King
2019-06-10 10:44 ` René Scharfe
2019-06-13 19:16 ` Jeff King
2019-04-13 22:16 ` brian m. carlson
2019-04-15 21:36 ` Jeff King
2019-04-26 14:54 ` Johannes Schindelin
2019-05-02 20:20 ` Ævar Arnfjörð Bjarmason
2019-05-03 20:49 ` Johannes Schindelin
2019-05-03 20:52 ` Jeff King
2019-04-26 14:47 ` Johannes Schindelin
[not found] ` <pull.145.v2.git.gitgitgadget@gmail.com>
[not found] ` <4ea94a8784876c3a19e387537edd81a957fc692c.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:29 ` [PATCH v2 3/4] archive: optionally use zlib directly for gzip compression René Scharfe
[not found] ` <ac2b2488a1b42b3caf8a84594c48eca796748e59.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:30 ` [PATCH v2 2/4] archive-tar: mark RECORDSIZE/BLOCKSIZE as unsigned René Scharfe
2019-05-08 11:45 ` Johannes Schindelin
2019-05-08 23:04 ` Jeff King
2019-05-09 14:06 ` Johannes Schindelin
2019-05-09 18:38 ` Jeff King
2019-05-10 17:18 ` René Scharfe
2019-05-10 21:20 ` Jeff King
2022-06-12 6:00 ` [PATCH v3 0/5] Avoid spawning gzip in git archive René Scharfe
2022-06-12 6:03 ` [PATCH v3 1/5] archive: rename archiver data field to filter_command René Scharfe
2022-06-12 6:05 ` [PATCH v3 2/5] archive-tar: factor out write_block() René Scharfe
2022-06-12 6:08 ` [PATCH v3 3/5] archive-tar: add internal gzip implementation René Scharfe
2022-06-13 19:10 ` Junio C Hamano
2022-06-12 6:18 ` [PATCH v3 4/5] archive-tar: use OS_CODE 3 (Unix) for internal gzip René Scharfe
2022-06-12 6:19 ` [PATCH v3 5/5] archive-tar: use internal gzip by default René Scharfe
2022-06-13 21:55 ` Junio C Hamano
2022-06-14 11:27 ` Johannes Schindelin
2022-06-14 15:47 ` René Scharfe
2022-06-14 15:56 ` René Scharfe
2022-06-14 16:29 ` Johannes Schindelin
2022-06-14 20:04 ` René Scharfe
2022-06-15 16:41 ` Junio C Hamano
2022-06-14 11:28 ` [PATCH v3 0/5] Avoid spawning gzip in git archive Johannes Schindelin
2022-06-14 20:05 ` René Scharfe
2022-06-30 18:55 ` Johannes Schindelin
2022-07-01 16:05 ` Johannes Schindelin
2022-07-01 16:27 ` Jeff King
2022-07-01 17:47 ` Junio C Hamano
2022-06-15 16:53 ` [PATCH v4 0/6] " René Scharfe
2022-06-15 16:58 ` [PATCH v4 1/6] archive: update format documentation René Scharfe
2022-06-15 16:59 ` [PATCH v4 2/6] archive: rename archiver data field to filter_command René Scharfe
2022-06-15 17:01 ` [PATCH v4 3/6] archive-tar: factor out write_block() René Scharfe
2022-06-15 17:02 ` [PATCH v4 4/6] archive-tar: add internal gzip implementation René Scharfe
2022-06-15 20:32 ` Ævar Arnfjörð Bjarmason
2022-06-16 18:55 ` René Scharfe
2022-06-24 11:13 ` Ævar Arnfjörð Bjarmason
2022-06-24 20:24 ` René Scharfe
2022-06-15 17:04 ` [PATCH v4 5/6] archive-tar: use OS_CODE 3 (Unix) for internal gzip René Scharfe
2022-06-15 17:05 ` [PATCH v4 6/6] archive-tar: use internal gzip by default René Scharfe
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