kvm tools: Make raw block device work

Previously, we use mmaped host root partition as guest's root
filesystem. As virtio-9p based root filesystem is supported,
mmaped host root partition approach is not used anymore.

It is useful to use raw block device as guest's disk backend for some
user. e.g. bypass host's fs layer.

This patch makes raw block device work as disk image, user can do
read/write on raw block device, by using DISK_IMAGE_REGULAR instead of
DISK_IMAGE_MMAP for block device

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/tools/kvm/disk/blk.c b/tools/kvm/disk/blk.c
index 72c17225538ed1a1bb4f973b669b7da62e6521b6..1b0615535d132cf262eacbc7587b75e661335aef 100644 (file)
--- a/tools/kvm/disk/blk.c
+++ b/tools/kvm/disk/blk.c
@@ -1,29 +1,58 @@
 #include "kvm/disk-image.h"
 
 #include <linux/err.h>
+#include <mntent.h>
 
 /*
  * raw image and blk dev are similar, so reuse raw image ops.
  */
 static struct disk_image_operations blk_dev_ops = {
-       .read_sector            = raw_image__read_sector,
-       .write_sector           = raw_image__write_sector,
-       .close                  = raw_image__close,
+       .read_sector    = raw_image__read_sector,
+       .write_sector   = raw_image__write_sector,
 };
 
+static bool is_mounted(struct stat *st)
+{
+       struct stat st_buf;
+       struct mntent *mnt;
+       FILE *f;
+
+       f = setmntent("/proc/mounts", "r");
+       if (!f)
+               return false;
+
+       while ((mnt = getmntent(f)) != NULL) {
+               if (stat(mnt->mnt_fsname, &st_buf) == 0 &&
+                   S_ISBLK(st_buf.st_mode) && st->st_rdev == st_buf.st_rdev) {
+                       fclose(f);
+                       return true;
+               }
+       }
+
+       fclose(f);
+       return false;
+}
+
 struct disk_image *blkdev__probe(const char *filename, struct stat *st)
 {
-       u64 size;
+       struct disk_image *disk;
        int fd, r;
+       u64 size;
 
        if (!S_ISBLK(st->st_mode))
                return ERR_PTR(-EINVAL);
 
+       if (is_mounted(st)) {
+               pr_err("Block device %s is already mounted! Unmount before use.",
+                      filename);
+               return ERR_PTR(-EINVAL);
+       }
+
        /*
         * Be careful! We are opening host block device!
         * Open it readonly since we do not want to break user's data on disk.
         */
-       fd = open(filename, O_RDONLY);
+       fd = open(filename, O_RDWR);
        if (fd < 0)
                return ERR_PTR(fd);
 
@@ -38,5 +67,10 @@ struct disk_image *blkdev__probe(const char *filename, struct stat *st)
         * mmap large disk. There is not enough virtual address space
         * in 32-bit host. However, this works on 64-bit host.
         */
-       return disk_image__new(fd, size, &blk_dev_ops, DISK_IMAGE_MMAP);
+       disk = disk_image__new(fd, size, &blk_dev_ops, DISK_IMAGE_REGULAR);
+#ifdef CONFIG_HAS_AIO
+               if (!IS_ERR_OR_NULL(disk))
+                       disk->async = 1;
+#endif
+       return disk;
 }