On 11/03/2015 12:11 AM, Vladimir Sementsov-Ogievskiy wrote:
On 02.11.2015 12:13, Xiao Guangrong wrote:
lseek can not work for all block devices as the man page says:
| Some devices are incapable of seeking and POSIX does not specify
| which devices must support lseek().

This patch tries to add the support on Linux by using BLKGETSIZE64

Signed-off-by: Xiao Guangrong <guangrong.x...@linux.intel.com>
  util/osdep.c | 20 ++++++++++++++++++++
  1 file changed, 20 insertions(+)

diff --git a/util/osdep.c b/util/osdep.c
index 5a61e19..b20c793 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -45,6 +45,11 @@
  extern int madvise(caddr_t, size_t, int);
+#include <sys/ioctl.h>
+#include <linux/fs.h>
  #include "qemu-common.h"
  #include "qemu/sockets.h"
  #include "qemu/error-report.h"
@@ -433,6 +438,21 @@ int64_t qemu_fd_getlength(int fd)
      int64_t size;
+    struct stat stat_buf;
+    if (fstat(fd, &stat_buf) < 0) {
+        return -errno;
+    }
+    if ((S_ISBLK(stat_buf.st_mode)) && !ioctl(fd, BLKGETSIZE64, &size)) {
+        /* The size of block device is larger than max int64_t? */
+        if (size < 0) {
+            return -EOVERFLOW;
+        }
+        return size;
+    }
      size = lseek(fd, 0, SEEK_END);
      if (size < 0) {
          return -errno;

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>

just a question: is there any use for stat.st_size ? Is it always worse then 

The man page says:
The  st_size field gives the size of the file (if it is a regular file or a 
symbolic link)
in bytes.  The size of a symbolic link is the length of the pathname it 
contains, without a
terminating null byte.

So it can not work on symbolic link.

Does it work for

Quickly checked with a program written by myself and 'stat' command, the answer 
is NO. :)

also, "This patch tries to add..". Hmm. It looks like this patch is not sure 
about will it success.
I'd prefer "This patch adds", but this is not important

Thanks for your sharing. I did not know the different, now, i got it. :)

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