Add host_device support to qemu-img. (Nolan Leake)

This patch allows the use a host_device as the destination for "qemu-img
convert".

I added a ->bdrv_create function host_device.  It merely verifies that
the device exists and is large enough.

A check is needed in the qemu-img convert loop to ensure that we write
out all 0 sectors to the host_device.  Otherwise they end up with stale
garbage where all zero sectors were expected.

I also made the check against bdrv_is_allocated enabled for everything
_except_ host devices, since there is no point in making the block
backend write a bunch of zeros just so that we can memcmp them
immediately afterwards.  Host devices can't benefit from this because
there is no way to differentiate between a sector being unallocated
because it was never written, or because it was written with all zeros
and then made a trip through qemu-img convert.

Finally, there is an unrelated fix for a typo in the error message
printed if the destination device does not support ->bdrv_create.

Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6978 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 36 insertions, 0 deletions

diff --git a/block-raw-posix.c b/block-raw-posix.c
index 4874b8e4a4..bff822ea65 100644
--- a/block-raw-posix.c
+++ b/block-raw-posix.c
@@ -1378,11 +1378,47 @@ static BlockDriverAIOCB *raw_aio_ioctl(BlockDriverState *bs,
 }
 #endif /* !linux && !FreeBSD */
 
+#if defined(__linux__) || defined(__FreeBSD__)
+static int hdev_create(const char *filename, int64_t total_size,
+                       const char *backing_file, int flags)
+{
+    int fd;
+    int ret = 0;
+    struct stat stat_buf;
+
+    if (flags || backing_file)
+        return -ENOTSUP;
+
+    fd = open(filename, O_WRONLY | O_BINARY);
+    if (fd < 0)
+        return -EIO;
+
+    if (fstat(fd, &stat_buf) < 0)
+        ret = -EIO;
+    else if (!S_ISBLK(stat_buf.st_mode))
+        ret = -EIO;
+    else if (lseek(fd, 0, SEEK_END) < total_size * 512)
+        ret = -ENOSPC;
+
+    close(fd);
+    return ret;
+}
+
+#else  /* !(linux || freebsd) */
+
+static int hdev_create(const char *filename, int64_t total_size,
+                       const char *backing_file, int flags)
+{
+    return -ENOTSUP;
+}
+#endif
+
 BlockDriver bdrv_host_device = {
     .format_name	= "host_device",
     .instance_size	= sizeof(BDRVRawState),
     .bdrv_open		= hdev_open,
     .bdrv_close		= raw_close,
+    .bdrv_create        = hdev_create,
     .bdrv_flush		= raw_flush,
 
 #ifdef CONFIG_AIO