Re: [PATCH 2/3] util: add xtalloc.[ch]

[Austin Clements <amdragon@MIT.EDU>]

Quoth david@tethera.net on Dec 16 at 11:24 pm:
> From: David Bremner <bremner@debian.org>
> 
> These are intended to be simple wrappers to provide slightly better
> debugging information than what talloc currently provides natively.
> ---
>  notmuch-client.h    |    2 +-
>  util/Makefile.local |    2 +-
>  util/xtalloc.c      |   15 +++++++++++++++
>  util/xtalloc.h      |   18 ++++++++++++++++++
>  4 files changed, 35 insertions(+), 2 deletions(-)
>  create mode 100644 util/xtalloc.c
>  create mode 100644 util/xtalloc.h
> 
> diff --git a/notmuch-client.h b/notmuch-client.h
> index d7b352e..60be030 100644
> --- a/notmuch-client.h
> +++ b/notmuch-client.h
> @@ -58,7 +58,7 @@ typedef GMimeCipherContext notmuch_crypto_context_t;
>  #include <errno.h>
>  #include <signal.h>
>  
> -#include <talloc.h>
> +#include "xtalloc.h"
>  
>  #define unused(x) x __attribute__ ((unused))
>  
> diff --git a/util/Makefile.local b/util/Makefile.local
> index a11e35b..8a62c00 100644
> --- a/util/Makefile.local
> +++ b/util/Makefile.local
> @@ -4,7 +4,7 @@ dir := util
>  extra_cflags += -I$(srcdir)/$(dir)
>  
>  libutil_c_srcs := $(dir)/xutil.c $(dir)/error_util.c $(dir)/hex-escape.c \
> -		  $(dir)/string-util.c
> +		  $(dir)/string-util.c $(dir)/xtalloc.c
>  
>  libutil_modules := $(libutil_c_srcs:.c=.o)
>  
> diff --git a/util/xtalloc.c b/util/xtalloc.c
> new file mode 100644
> index 0000000..22834bd
> --- /dev/null
> +++ b/util/xtalloc.c
> @@ -0,0 +1,15 @@
> +#include <string.h>
> +#include "xtalloc.h"
> +
> +char *
> +xtalloc_strndup_named_const (void *ctx, const char *str,
> +			     size_t len, const char *name)
> +{
> +    char *ptr = talloc_named_const (ctx, len + 1, name);
> +
> +    if (ptr) {
> +	memcpy (ptr, str, len);

This isn't safe.  If the string at ptr is actually shorter than len,
this may read past allocated memory and crash.

Maybe this should just call talloc_strndup and talloc_set_name_const?

> +	*(ptr + len) = '\0';
> +    }
> +    return ptr;
> +}
> diff --git a/util/xtalloc.h b/util/xtalloc.h
> new file mode 100644
> index 0000000..3cc1179
> --- /dev/null
> +++ b/util/xtalloc.h
> @@ -0,0 +1,18 @@
> +#ifndef _XTALLOC_H
> +#define _XTALLOC_H
> +
> +#include <talloc.h>
> +
> +/* Like talloc_strndup, but take an extra parameter for the internal talloc
> + * name (for debugging) */
> +
> +char *
> +xtalloc_strndup_named_const (void *ctx, const char *str,
> +			     size_t len, const char *name);

I agree with Tomi that these shouldn't be named with 'x'.  For this
one, it seems fine to simply drop the 'x', since the name is fully
descriptive of what it does.

> +
> +/* use the __location__ macro from talloc.h to name a string according to its
> + * source location */
> +
> +#define xtalloc_strndup(ctx, str, len) xtalloc_strndup_named_const (ctx, str, len, __location__)

For this, what about talloc_strndup_debug?

> +
> +#endif