From: Torsten Bögershausen Date: Mon, 29 Jun 2015 04:48:16 GMT Subject: Re: [PATCH v4 01/44] wrapper: implement xopen() 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: > 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 > Helped-by: Jeff King > Signed-off-by: Paul Tan > --- > 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. 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); +