[libvirt] [PATCH v3 3/5] osdep: Enable qemu_open to dup pre-opened fd

[Corey Bryant]

This patch adds support to qemu_open to dup(fd) a pre-opened file
descriptor if the filename is of the format /dev/fd/X.

This can be used when QEMU is restricted from opening files, and
the management application opens files on QEMU's behalf.

If the fd was passed to the monitor with the pass-fd command, it
must be explicitly closed with the 'closefd' command when it is
no longer required, in order to prevent fd leaks.

Signed-off-by: Corey Bryant <coreyb at linux.vnet.ibm.com>
---
v2:
 -Get rid of file_open and move dup code to qemu_open
  (kwolf at redhat.com)
 -Use strtol wrapper instead of atoi (kwolf at redhat.com)

v3:
 -Add note about fd leakage (eblake at redhat.com)

 osdep.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/osdep.c b/osdep.c
index 3e6bada..c17cdcb 100644
--- a/osdep.c
+++ b/osdep.c
@@ -82,6 +82,19 @@ int qemu_open(const char *name, int flags, ...)
     int ret;
     int mode = 0;
 
+#ifndef _WIN32
+    const char *p;
+
+    /* Attempt dup of fd for pre-opened file */
+    if (strstart(name, "/dev/fd/", &p)) {
+        ret = qemu_parse_fd(p);
+        if (ret == -1) {
+            return -1;
+        }
+        return dup(ret);
+    }
+#endif
+
     if (flags & O_CREAT) {
         va_list ap;
 
-- 
1.7.10.2