[Qemu-devel] [PATCH v2] block/raw-posix: Linux compat-ioctl warning workaround

[Johannes Stezenbach <js@sig21.net>]

On Linux x86_64 host with 32bit userspace, running
qemu or even just "qemu-img create -f qcow2 some.img 1G"
causes a kernel warning:

ioctl32(qemu-img:5296): Unknown cmd fd(3) cmd(00005326){t:'S';sz:0} arg(7fffffff) on some.img
ioctl32(qemu-img:5296): Unknown cmd fd(3) cmd(801c0204){t:02;sz:28} arg(fff77350) on some.img

ioctl 00005326 is CDROM_DRIVE_STATUS,
ioctl 801c0204 is FDGETPRM.

The warning appears because the Linux compat-ioctl handler for these
ioctls only applies to block devices, while qemu also uses the ioctls on
plain files.  Work around by calling fstat() the ensure the ioctls are
only used on block devices.

Signed-off-by: Johannes Stezenbach <js@sig21.net>
---
discussed in http://lkml.kernel.org/r/20110617090424.GA19345@sig21.net

I'll also send a Linux kernel patch but this is needed to
fix the warning on old kernels.

v2: changes according to review comments

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 4cd7d7a..34b64aa 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -46,6 +46,8 @@
 #include <sys/dkio.h>
 #endif
 #ifdef __linux__
+#include <sys/types.h>
+#include <sys/stat.h>
 #include <sys/ioctl.h>
 #include <sys/param.h>
 #include <linux/cdrom.h>
@@ -1188,6 +1190,7 @@ static int floppy_probe_device(const char *filename)
     int fd, ret;
     int prio = 0;
     struct floppy_struct fdparam;
+    struct stat st;
 
     if (strstart(filename, "/dev/fd", NULL))
         prio = 50;
@@ -1196,12 +1199,17 @@ static int floppy_probe_device(const char *filename)
     if (fd < 0) {
         goto out;
     }
+    ret = fstat(fd, &st);
+    if (ret == -1 || !S_ISBLK(st.st_mode)) {
+        goto outc;
+    }
 
     /* Attempt to detect via a floppy specific ioctl */
     ret = ioctl(fd, FDGETPRM, &fdparam);
     if (ret >= 0)
         prio = 100;
 
+outc:
     close(fd);
 out:
     return prio;
@@ -1290,17 +1298,23 @@ static int cdrom_probe_device(const char *filename)
 {
     int fd, ret;
     int prio = 0;
+    struct stat st;
 
     fd = open(filename, O_RDONLY | O_NONBLOCK);
     if (fd < 0) {
         goto out;
     }
+    ret = fstat(fd, &st);
+    if (ret == -1 || !S_ISBLK(st.st_mode)) {
+        goto outc;
+    }
 
     /* Attempt to detect via a CDROM specific ioctl */
     ret = ioctl(fd, CDROM_DRIVE_STATUS, CDSL_CURRENT);
     if (ret >= 0)
         prio = 100;
 
+outc:
     close(fd);
 out:
     return prio;