[Pkg-gnupg-commit] [libassuan] 05/14: Speedup closing fds before an exec.

[Daniel Kahn Gillmor]

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dkg pushed a commit to branch master
in repository libassuan.

commit e64f9a4af5a379f5a9fde59f0f944cd10ccfc6ea
Author: Werner Koch <wk at gnupg.org>
Date:   Wed Jul 13 15:33:41 2016 +0200

    Speedup closing fds before an exec.
    
    * src/system-posix.c [__linux__]: Include dirent.h.
    (get_max_fds) [__linux__]: Return the actual used highest fd.
    --
    
    This is the same code as introduced with the
    GnuPG commit 512c56af43027149e8beacf259746b8d7bf9b1a2
    
    Signed-off-by: Werner Koch <wk at gnupg.org>
---
 src/system-posix.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/src/system-posix.c b/src/system-posix.c
index 8ca27e6..52376da 100644
--- a/src/system-posix.c
+++ b/src/system-posix.c
@@ -36,6 +36,9 @@
 # include <sys/time.h>
 # include <sys/resource.h>
 #endif /*HAVE_GETRLIMIT*/
+#if __linux__
+# include <dirent.h>
+#endif /*__linux__ */
 
 
 #include "assuan-defs.h"
@@ -180,6 +183,43 @@ 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 faster
+   * than for example doing 4096 close calls where almost all of them
+   * will fail.  We use the same code in GnuPG and measured this: 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 the 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__
+  {
+    DIR *dir = NULL;
+    struct dirent *dir_entry;
+    const char *s;
+    int x;
+
+    dir = opendir ("/proc/self/fd");
+    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;

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