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greatly improve freopen behavior

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1. don't open /dev/null just as a basis to copy flags; use shared
__fmodeflags function to get the right file flags for the mode.

2. handle the case (probably invalid, but whatever) case where the
original stream's file descriptor was closed; previously, the logic
re-closed it.

3. accept the "e" mode flag for close-on-exec; update dup3 to fallback
to using dup2 so we can simply call __dup3 instead of putting fallback
logic in freopen itself.
This commit is contained in:
Rich Felker
2012-10-24 21:16:06 -04:00
parent 708c91f4e9
commit 892cafff66
5 changed files with 41 additions and 17 deletions
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17
src/stdio/freopen.c
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@ -7,24 +7,27 @@
/* Locking is not necessary because, in the event of failure, the stream
* passed to freopen is invalid as soon as freopen is called. */
int __dup3(int, int, int);
FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict f)
{
int fl;
int fl = __fmodeflags(mode);
FILE *f2;
fflush(f);
if (!filename) {
f2 = fopen("/dev/null", mode);
if (!f2) goto fail;
fl = __syscall(SYS_fcntl, f2->fd, F_GETFL, 0);
if (fl&O_CLOEXEC)
__syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
goto fail2;
goto fail;
return f;
} else {
f2 = fopen(filename, mode);
if (!f2) goto fail;
if (syscall(SYS_dup2, f2->fd, f->fd) < 0)
goto fail2;
if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
}
f->flags = (f->flags & F_PERM) | f2->flags;