Avoid running into nonexistent system calls repeatedly.

diff --git a/ChangeLog b/ChangeLog
index a24ed56..efac0df 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2009-08-23  Bruno Haible  <bruno@clisp.org>
 
+       * lib/dup3.c (dup3): Test only once whether the system actually exists.
+       * lib/pipe2.c (pipe2): Likewise.
+       Suggested by Eric Blake.
+
+2009-08-23  Bruno Haible  <bruno@clisp.org>
+
        Tolerate declared but missing dup3 syscall.
        * lib/dup3.c (dup3): Invoke original dup3 function first, if available.
        * lib/unistd.in.h (dup3): If the function is already present,

diff --git a/lib/dup3.c b/lib/dup3.c
index 62cdb53..906594e 100644 (file)
--- a/lib/dup3.c
+++ b/lib/dup3.c
@@ -53,9 +53,18 @@ dup3 (int oldfd, int newfd, int flags)
   /* Try the system call first, if it exists.  (We may be running with a glibc
      that has the function but with an older kernel that lacks it.)  */
   {
-    int result = dup3 (oldfd, newfd, flags);
-    if (!(result < 0 && errno == ENOSYS))
-      return result;
+    /* Cache the information whether the system call really exists.  */
+    static int have_dup3_really; /* 0 = unknown, 1 = yes, -1 = no */
+    if (have_dup3_really >= 0)
+      {
+       int result = dup3 (oldfd, newfd, flags);
+       if (!(result < 0 && errno == ENOSYS))
+         {
+           have_dup3_really = 1;
+           return result;
+         }
+       have_dup3_really = -1;
+      }
   }
 #endif
 

diff --git a/lib/pipe2.c b/lib/pipe2.c
index c18860d..d3b612d 100644 (file)
--- a/lib/pipe2.c
+++ b/lib/pipe2.c
@@ -45,9 +45,18 @@ pipe2 (int fd[2], int flags)
   /* Try the system call first, if it exists.  (We may be running with a glibc
      that has the function but with an older kernel that lacks it.)  */
   {
-    int result = pipe2 (fd, flags);
-    if (!(result < 0 && errno == ENOSYS))
-      return result;
+    /* Cache the information whether the system call really exists.  */
+    static int have_pipe2_really; /* 0 = unknown, 1 = yes, -1 = no */
+    if (have_pipe2_really >= 0)
+      {
+       int result = pipe2 (fd, flags);
+       if (!(result < 0 && errno == ENOSYS))
+         {
+           have_pipe2_really = 1;
+           return result;
+         }
+       have_pipe2_really = -1;
+      }
   }
 #endif