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Re: [Xen-devel] [PATCH] xl: Return an error if an empty file is passed to cd-insert

On 13/05/13 10:35, Roger Pau Monné wrote:
On 10/05/13 17:43, George Dunlap wrote:
Two changes:
* Stat the file before calling libxl_cdrom_insert()
* Return an error if anything fails (including libxl_cdrom_insert)

This is in part to work around the fact that the RAW disk type
is used for things that aren't actually files; so we can't call
stat in libxl_device.c:libxl__device_disk_set_backend() because
it may be going over a remote protocol.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
  tools/libxl/xl_cmdimpl.c |   26 +++++++++++++++++++++-----
  1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index c1a969b..e8ce35b 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -2505,25 +2505,42 @@ int main_memset(int argc, char **argv)
      return 0;
-static void cd_insert(uint32_t domid, const char *virtdev, char *phys)
+static int cd_insert(uint32_t domid, const char *virtdev, char *phys)
      libxl_device_disk disk; /* we don't free disk's contents */
      char *buf = NULL;
      XLU_Config *config = 0;
+    struct stat b;
+    int rc = 0;
if (asprintf(&buf, "vdev=%s,access=r,devtype=cdrom,target=%s",
                   virtdev, phys ? phys : "") < 0) {
          fprintf(stderr, "out of memory\n");
-        return;
+        return 1;

If this were a library function I would definitely return -ERROR_NOMEM; but since this is just a helper function whose value is going to be returned to the command-line, I think just returning 1 is the best thing to do.

parse_disk_config(&config, buf, &disk); - libxl_cdrom_insert(ctx, domid, &disk, NULL);
+    /* ATM the existence of the backing file is not checked for qdisk
+     * in libxl_cdrom_insert() because RAW is used for remote
+     * protocols as well as plain files.  This will ideally be changed
+     * for 4.4, but this work-around fixes the problem of "cd-insert"
+     * returning success for non-existent files. */
+    if (disk.format != LIBXL_DISK_FORMAT_EMPTY
+        && stat(disk.pdev_path, &b)) {
+        fprintf(stderr, "Cannot stat file: %s\n",
+                disk.pdev_path);
You are leaking buf here, I know xl is just about to exit, but it might
be best to to define a label below that contains:

Oops!  Sorry about that...

+        return 1;

+    }
+    if (libxl_cdrom_insert(ctx, domid, &disk, NULL))
+        rc=1;
You could use the return value of libxl_cdrom_insert instead of 1.

I sort of assumed that libxl_cdrom_insert() was a negative value, and that I wanted xl to return 1.

I'll send a respin w/ the leak fixed.


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