Re: [PATCH v4 01/44] wrapper: implement xopen()
- From
Torsten Bögershausen <tboegi@web.de>
- Date
- Jun 29, 2015, 04:48 UTC
- Message-ID
- <5590CE10.3020104@web.de>
- In-Reply-To
- <1435500366-31700-2-git-send-email-pyokagan@gmail.com>
On 06/28/2015 04:05 PM, Paul Tan wrote:
Show 53 quoted lines
> A common usage pattern of open() is to check if it was successful, and
> die() if it was not:
>
> int fd = open(path, O_WRONLY | O_CREAT, 0777);
> if (fd < 0)
> die_errno(_("Could not open '%s' for writing."), path);
>
> Implement a wrapper function xopen() that does the above so that we can
> save a few lines of code, and make the die() messages consistent.
>
> Helped-by: Torsten Bögershausen <tboegi@web.de>
> Helped-by: Jeff King <peff@peff.net>
> Signed-off-by: Paul Tan <pyokagan@gmail.com>
> ---
> git-compat-util.h | 1 +
> wrapper.c | 25 +++++++++++++++++++++++++
> 2 files changed, 26 insertions(+)
>
> diff --git a/git-compat-util.h b/git-compat-util.h
> index c6d391f..e168dfd 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -717,6 +717,7 @@ extern void *xrealloc(void *ptr, size_t size);
> extern void *xcalloc(size_t nmemb, size_t size);
> extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
> extern void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);
> +extern int xopen(const char *path, int flags, ...);
> extern ssize_t xread(int fd, void *buf, size_t len);
> extern ssize_t xwrite(int fd, const void *buf, size_t len);
> extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
> diff --git a/wrapper.c b/wrapper.c
> index ff49807..7e13ae0 100644
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -189,6 +189,31 @@ void *xcalloc(size_t nmemb, size_t size)
> # endif
> #endif
>
> +/**
> + * xopen() is the same as open(), but it die()s if the open() fails.
> + */
> +int xopen(const char *path, int oflag, ...)
> +{
> + mode_t mode = 0;
> + va_list ap;
> +
> + va_start(ap, oflag);
> + if (oflag & O_CREAT)
> + mode = va_arg(ap, mode_t);
> + va_end(ap);
> +
> + assert(path);
> +2 remarks: - I don't know if and why we need the assert() here (but don't know if we have a strategie in Git for assert()) - Having xopen() with 2 or 3 parameter is good, but the current may need some tweaks for better portability:
int xopen(const char *path, int oflag, ...)
{
mode_t mode = 0;
if (oflag & O_CREAT) {
va_list ap;
va_start(ap, oflag);
mode = va_arg(ap, int);
va_end(ap);}
See e.g. <http://blitiri.com.ar/git/r/libfiu/c/37f6a98110e3bb59bbb4971241baa3a385c3f724/> why va_arg(ap, int) should be used:
+ + /* va_arg() can only take fully promoted types, and mode_t + * sometimes is smaller than an int, so we should always pass + * int to it, and not mode_t. Not doing so would may result in + * a compile-time warning and run-time error. We asume that it + * is never bigger than an int, which holds in practise. */ + mode = va_arg(l, int); +