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common: Speedup closing fds before an exec.

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* common/exechelp-posix.c [__linux__]: Include dirent.h.
(get_max_fds) [__linux__]: Return the actual used highest fd.
--

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2016-05-27 22:02:54 +02:00
parent ad75ca9c96
commit 512c56af43
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GPG Key ID: E3FDFF218E45B72B
1 changed files with 44 additions and 0 deletions
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44
common/exechelp-posix.c
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@ -67,6 +67,11 @@
# include <sys/stat.h>
#endif
#if __linux__
# include <sys/types.h>
# include <dirent.h>
#endif /*__linux__ */
#include "util.h"
#include "i18n.h"
#include "sysutils.h"
@ -97,6 +102,45 @@ get_max_fds (void)
#ifdef HAVE_GETRLIMIT
struct rlimit rl;
/* Under Linux we can figure out the highest used file descriptor by
* reading /proc/PID/fd. This is in the common cases much fast than
* for example doing 4096 close calls where almost all of them will
* fail. On a system with a limit of 4096 files and only 8 files
* open with the highest number being 10, we speedup close_all_fds
* from 125ms to 0.4ms including readdir.
*
* Another option would be to close the file descriptors as returned
* from reading that directory - however then we need to snapshot
* that list before starting to close them. */
#ifdef __linux__
{
char dirname[50];
DIR *dir = NULL;
struct dirent *dir_entry;
const char *s;
int x;
snprintf (dirname, sizeof dirname, "/proc/%u/fd", (unsigned int)getpid ());
dir = opendir (dirname);
if (dir)
{
while ((dir_entry = readdir (dir)))
{
s = dir_entry->d_name;
if ( *s < '0' || *s > '9')
continue;
x = atoi (s);
if (x > max_fds)
max_fds = x;
}
closedir (dir);
}
if (max_fds != -1)
return max_fds + 1;
}
#endif /* __linux__ */
# ifdef RLIMIT_NOFILE
if (!getrlimit (RLIMIT_NOFILE, &rl))
max_fds = rl.rlim_max;