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From: Jeff King <peff@peff.net>
To: "Martin Ågren" <martin.agren@gmail.com>
Cc: git@vger.kernel.org, "brian m . carlson" <sandals@crustytoothpaste.net>
Subject: Re: [PATCH v3 2/2] setup: fix memory leaks with `struct repository_format`
Date: Wed, 23 Jan 2019 00:57:05 -0500	[thread overview]
Message-ID: <20190123055704.GA19601@sigill.intra.peff.net> (raw)
In-Reply-To: <f8b021033b887923662eb9fa63f6df1677ebbbb5.1548186510.git.martin.agren@gmail.com>

On Tue, Jan 22, 2019 at 10:45:48PM +0100, Martin Ågren wrote:

> Call `clear_...()` at the start of `read_...()` instead of just zeroing
> the struct, since we sometimes enter the function multiple times. This
> means that it is important to initialize the struct before calling
> `read_...()`, so document that.

This part is a little counter-intuitive to me. Is anybody ever going to
pass in anything except a struct initialized to REPOSITORY_FORMAT_INIT?

If so, might it be kinder for read_...() to not assume anything about
the incoming struct, and initialize it from scratch? I.e., not to use
clear() but just do the initialization step?

A caller which calls read_() multiple times would presumably have an
intervening clear (either their own, or the one done on an error return
from the read function).

Other than that minor nit, I like the overall shape of this.

One interesting tidbit:

> +/*
> + * Always use this to initialize a `struct repository_format`
> + * to a well-defined, default state before calling
> + * `read_repository()`.
> + */
> +#define REPOSITORY_FORMAT_INIT \
> +{ \
> +	.version = -1, \
> +	.is_bare = -1, \
> +	.hash_algo = GIT_HASH_SHA1, \
> +	.unknown_extensions = STRING_LIST_INIT_DUP, \
> +}
> [...]
> +	struct repository_format candidate = REPOSITORY_FORMAT_INIT;

This uses designated initializers, which is a C99-ism, but one we've
used previously and feel confident in. But...

> +void clear_repository_format(struct repository_format *format)
> +{
> +	string_list_clear(&format->unknown_extensions, 0);
> +	free(format->work_tree);
> +	free(format->partial_clone);
> +	*format = (struct repository_format)REPOSITORY_FORMAT_INIT;
> +}

...this uses that expression not as an initializer, but as a compound
literal. That's also C99, but AFAIK it's the first usage in our code
base. I don't know if it will cause problems or not.

The "old" way to do it is:

  struct repository_format foo = REPOSITORY_FORMAT_INIT;
  memcpy(format, &foo, sizeof(foo));

Given how simple it is to fix if it turns out to be a problem, I'm OK
including it as a weather balloon.

-Peff

  reply	other threads:[~2019-01-23  5:57 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-18  7:25 [PATCH 0/3] setup: add `clear_repository_format()` Martin Ågren
2018-12-18  7:25 ` [PATCH 1/3] setup: drop return value from `read_repository_format()` Martin Ågren
2018-12-19 15:27   ` Jeff King
2018-12-19 21:42     ` Martin Ågren
2018-12-20  0:17     ` brian m. carlson
2018-12-20  2:52       ` Jeff King
2018-12-20  3:45         ` brian m. carlson
2018-12-20 14:53           ` Jeff King
2018-12-18  7:25 ` [PATCH 2/3] setup: do not use invalid `repository_format` Martin Ågren
2018-12-19  0:18   ` brian m. carlson
2018-12-19 21:43     ` Martin Ågren
2018-12-19 15:38   ` Jeff King
2018-12-19 21:46     ` Martin Ågren
2018-12-19 23:17       ` Jeff King
2018-12-20  0:21     ` brian m. carlson
2018-12-18  7:25 ` [PATCH 3/3] setup: add `clear_repository_format()` Martin Ågren
2018-12-19 15:48   ` Jeff King
2018-12-19 21:49     ` Martin Ågren
2019-01-14 18:34 ` [PATCH v2 0/3] " Martin Ågren
2019-01-14 18:34   ` [PATCH v2 1/3] setup: free old value before setting `work_tree` Martin Ågren
2019-01-14 18:34   ` [PATCH v2 2/3] setup: do not use invalid `repository_format` Martin Ågren
2019-01-15 19:31     ` Jeff King
2019-01-17  6:31       ` Martin Ågren
2019-01-22  7:07         ` Jeff King
2019-01-22 13:34           ` Martin Ågren
2019-01-22 21:45             ` [PATCH v3 0/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-01-22 21:45               ` [PATCH v3 1/2] setup: free old value before setting `work_tree` Martin Ågren
2019-01-22 21:45               ` [PATCH v3 2/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-01-23  5:57                 ` Jeff King [this message]
2019-01-24  0:14                   ` brian m. carlson
2019-01-25 19:25                     ` Martin Ågren
2019-01-25 19:24                   ` Martin Ågren
2019-01-25 19:51                     ` Jeff King
2019-02-25 19:21                       ` Martin Ågren
2019-02-26 17:46                         ` Jeff King
2019-02-28 20:36                           ` [PATCH v4 0/2] " Martin Ågren
2019-02-28 20:36                             ` [PATCH v4 1/2] setup: free old value before setting `work_tree` Martin Ågren
2019-02-28 20:36                             ` [PATCH v4 2/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-03-06  4:56                             ` [PATCH v4 0/2] " Jeff King
2019-01-14 18:34   ` [PATCH v2 3/3] setup: add `clear_repository_format()` Martin Ågren

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