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@xxxxxx>
Helped-by: Jeff King <peff@xxxxxxxx>
Helped-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
Helped-by: Junio C Hamano <gitster@xxxxxxxxx>
Signed-off-by: Paul Tan <pyokagan@xxxxxxxxx>
---
Notes:
v5
* Remove assert()s since we do not need to over-zealously check against
insane code.
* Use va_arg(va, int) instead of va_arg(va, mode_t) to guard against
undefined behavior if mode_t is incompatible with the promoted integer
argument (int).
* The read/write error messages have returned as they can be used to
better diagnose permission errors. Hopefully I got the logic right
this time.
git-compat-util.h | 1 +
wrapper.c | 35 +++++++++++++++++++++++++++++++++++
2 files changed, 36 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..0a4502d 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -189,6 +189,41 @@ 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_arg() will have undefined behavior if the specified type is not
+ * compatible with the argument type. Since integers are promoted to
+ * ints, we fetch the next argument as an int, and then cast it to a
+ * mode_t to avoid undefined behavior.
+ */
+ va_start(ap, oflag);
+ if (oflag & O_CREAT)
+ mode = va_arg(ap, int);
+ va_end(ap);
+
+ for (;;) {
+ int fd = open(path, oflag, mode);
+ if (fd >= 0)
+ return fd;
+ if (errno == EINTR)
+ continue;
+
+ if ((oflag & O_RDWR) == O_RDWR)
+ die_errno(_("could not open '%s' for reading and writing"), path);
+ else if ((oflag & O_WRONLY) == O_WRONLY)
+ die_errno(_("could not open '%s' for writing"), path);
+ else
+ die_errno(_("could not open '%s' for reading"), path);
+ }
+}
+
/*
* xread() is the same a read(), but it automatically restarts read()
* operations with a recoverable error (EAGAIN and EINTR). xread()
--
2.5.0.rc1.76.gf60a929
--
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