1 files changed, 64 insertions, 0 deletions
diff --git a/src/execline/fdreserve.c b/src/execline/fdreserve.c
new file mode 100644
index 0000000..2df721a
--- /dev/null
+++ b/src/execline/fdreserve.c
@@ -0,0 +1,64 @@
+/* ISC license. */
+
+#include <unistd.h>
+#include <sys/resource.h>
+#include <skalibs/uint.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/env.h>
+#include <skalibs/djbunix.h>
+
+#define USAGE "fdreserve n prog..."
+
+#define MAXFDS 1024
+
+unsigned int doit (char *modif, unsigned int i, int fd)
+{
+  register unsigned int pos = 2 ;
+  modif[0] = 'F' ; modif[1] = 'D' ;
+  pos += uint_fmt(modif + pos, i) ;
+  modif[pos++] = '=' ;
+  pos += uint_fmt(modif + pos, (unsigned int)fd) ;
+  modif[pos++] = 0 ;
+  return pos ;
+}
+
+int main (int argc, char const *const *argv, char const *const *envp)
+{
+  unsigned int n ;
+  PROG = "fdreserve" ;
+  if ((argc < 3) || !uint0_scan(argv[1], &n))
+    strerr_dieusage(100, USAGE) ;
+  {
+    struct rlimit lim ;
+    if (getrlimit(RLIMIT_NOFILE, &lim) < 0) strerr_diefu1sys(111, "getrlimit") ;
+    if (n > lim.rlim_cur) strerr_dief1x(100, "too many requested fds") ;
+  }
+  {
+    char modif[12 * n] ;  /* enough for n times "FDaaaa=bbbb\0" */
+    unsigned int j = 0 ;
+    {
+      int fd[n >> 1][2] ;
+      register unsigned int i = 0 ;
+      for (; i < (n>>1) ; i++)
+        if (pipe(fd[i]) < 0)
+          strerr_diefu1sys(111, "reserve fds") ;
+      if (n & 1)
+      {
+        register int lastfd = open_read("/dev/null") ;
+        if (lastfd < 0)
+          strerr_diefu1sys(111, "reserve last fd") ;
+        fd_close(lastfd) ;
+        j += doit(modif + j, n-1, lastfd) ;
+      }
+      for (i = 0 ; i < (n>>1) ; i++)
+      {
+        fd_close(fd[i][0]) ;
+        fd_close(fd[i][1]) ;
+        j += doit(modif + j, i<<1, fd[i][0]) ;
+        j += doit(modif + j, (i<<1)|1, fd[i][1]) ;
+      }
+    }
+    pathexec_r(argv+2, envp, env_len(envp), modif, j) ;
+  }
+  strerr_dieexec(111, argv[2]) ;
+}