Re: [PATCH v3 2/2] setup: fix memory leaks with `struct repository_format`
- From
Jeff King <peff@peff.net>
- Date
- Jan 23, 2019, 05:57 UTC
- Message-ID
- <20190123055704.GA19601@sigill.intra.peff.net>
- 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:
Show 14 quoted lines
> +/*
> + * 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...
Show 7 quoted lines
> +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