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Set O_APPEND mode for stdout/stderr and output-sync temporary files.

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POSIX does not guarantee that writes will be atomic if a file is
opened for normal (non-append) output.  That means if multiple processes
are writing to the same file, output could be lost.  I can't think of
a real use-case where we would NOT want append for stdout/stderr, so
force it if we can.
This commit is contained in:
Paul Smith 2013-06-28 21:57:59 -04:00
parent 5e7bf7c554
commit 9453a7451d
4 changed files with 35 additions and 1 deletions
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9
ChangeLog
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@ -1,3 +1,10 @@
2013-06-28 Paul Smith <psmith@gnu.org>
* misc.c (set_append_mode): Set the O_APPEND flag on a file descriptor.
(open_tmpfd): Set append mode on the temporary file descriptor.
* main.c (main): Set append mode on stdout and stderr.
* makeint.h (set_append_mode): Declare it.
2013-06-22 Eli Zaretskii <eliz@gnu.org>
* build_w32.bat (LinkGCC): Prevent a comment from being displayed
@ -55,7 +62,7 @@
* main.c (verify_flag): Global variable to determine whether to
verify the database or not.
(decode_debug_flags): If debug mode, enable verify_flag.
(main): If MAKE_MAINTAINTER_MODE, enable verify_flag, otherwise not.
(main): If MAKE_MAINTAINER_MODE, enable verify_flag, otherwise not.
(die): Only verify the database if verify_flag is set.
* file.c (enter_file): Don't check caching unless verify_flag.
* makeint.h: Export verify_flag.

6
main.c
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@ -1195,6 +1195,12 @@ main (int argc, char **argv, char **envp)
setlinebuf (stdout);
#endif /* setlinebuf missing. */
/* Configure stdout/stderr to be in append mode.
This keeps parallel jobs from losing output due to overlapping writes. */
set_append_mode (fileno (stdout));
set_append_mode (fileno (stderr));
/* Figure out where this program lives. */
if (argv[0] == 0)

1
makeint.h
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@ -453,6 +453,7 @@ int alpha_compare (const void *, const void *);
void print_spaces (unsigned int);
char *find_percent (char *);
const char *find_percent_cached (const char **);
void set_append_mode (int);
int open_tmpfd (void);
FILE *open_tmpfile (char **, const char *);

20
misc.c
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@ -22,6 +22,11 @@ this program. If not, see <http://www.gnu.org/licenses/>. */
#include <stdarg.h>
#ifdef HAVE_FCNTL_H
# include <fcntl.h>
#else
# include <sys/file.h>
#endif
/* Compare strings *S1 and *S2.
Return negative if the first is less, positive if it is greater,
@ -897,6 +902,19 @@ get_path_max (void)
#endif
/* Set a file descriptor to be in O_APPEND mode.
If it fails, just ignore it. */
void
set_append_mode (int fd)
{
#if defined(F_GETFL) && defined(F_SETFL) && defined(O_APPEND)
int flags = fcntl (fd, F_GETFL, 0);
if (flags >= 0)
fcntl (fd, F_SETFL, flags | O_APPEND);
#endif
}
/* Provide support for temporary files. */
#ifndef HAVE_STDLIB_H
@ -928,6 +946,8 @@ open_tmpfd ()
fclose (tfile);
set_append_mode (fd);
return fd;
}