[Xen-devel] [PATCH] enforce read only on disks

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi all,
currently even if you specify 'r' for a disk on your VM config file,
qemu tries to open the file O_RDWR first.
This patch enforces that a disk with mode = 'r' on xenstore is actually
opened O_RDONLY.

Regards,

Stefano Stabellini

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff -r d2ff8a90436e block-raw-posix.c
--- a/block-raw-posix.c Tue Dec 16 16:03:12 2008 +0000
+++ b/block-raw-posix.c Mon Jan 05 17:16:34 2009 +0000
@@ -133,7 +133,6 @@
         open_flags |= O_RDWR;
     } else {
         open_flags |= O_RDONLY;
-        bs->read_only = 1;
     }
     if (flags & BDRV_O_CREAT)
         open_flags |= O_CREAT | O_TRUNC;
diff -r d2ff8a90436e block.c
--- a/block.c   Tue Dec 16 16:03:12 2008 +0000
+++ b/block.c   Mon Jan 05 17:16:34 2009 +0000
@@ -376,7 +376,6 @@
     char tmp_filename[PATH_MAX];
     char backing_filename[PATH_MAX];
 
-    bs->read_only = 0;
     bs->is_temporary = 0;
     bs->encrypted = 0;
 
@@ -444,12 +443,14 @@
     bs->total_sectors = 0; /* driver will set if it does not do getlength */
     if (bs->opaque == NULL && drv->instance_size > 0)
         return -1;
-    /* Note: for compatibility, we open disk image files as RDWR, and
-       RDONLY as fallback */
     if (!(flags & BDRV_O_FILE))
-        open_flags = BDRV_O_RDWR | (flags & BDRV_O_CACHE_MASK);
+        open_flags = flags & BDRV_O_CACHE_MASK;
     else
         open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
+    if (bs->read_only)
+        open_flags &= ~BDRV_O_RDWR;
+    else
+        open_flags |= BDRV_O_RDWR;
     ret = drv->bdrv_open(bs, filename, open_flags);
     if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
         ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
@@ -867,6 +868,11 @@
 int bdrv_is_read_only(BlockDriverState *bs)
 {
     return bs->read_only;
+}
+
+void bdrv_set_read_only(BlockDriverState *bs)
+{
+    bs->read_only = 1;
 }
 
 int bdrv_is_sg(BlockDriverState *bs)
diff -r d2ff8a90436e block.h
--- a/block.h   Tue Dec 16 16:03:12 2008 +0000
+++ b/block.h   Mon Jan 05 17:16:34 2009 +0000
@@ -125,6 +125,7 @@
 int bdrv_get_translation_hint(BlockDriverState *bs);
 int bdrv_is_removable(BlockDriverState *bs);
 int bdrv_is_read_only(BlockDriverState *bs);
+void bdrv_set_read_only(BlockDriverState *bs);
 int bdrv_is_sg(BlockDriverState *bs);
 int bdrv_is_inserted(BlockDriverState *bs);
 int bdrv_media_changed(BlockDriverState *bs);
diff -r d2ff8a90436e xenstore.c
--- a/xenstore.c        Tue Dec 16 16:03:12 2008 +0000
+++ b/xenstore.c        Mon Jan 05 17:16:34 2009 +0000
@@ -297,7 +297,7 @@
     char **e_danger = NULL;
     char *buf = NULL;
     char *fpath = NULL, *bpath = NULL,
-        *dev = NULL, *params = NULL, *drv = NULL;
+        *dev = NULL, *params = NULL, *mode = NULL, *drv = NULL;
     int i, any_hdN = 0, ret;
     unsigned int len, num, hd_index, pci_devid = 0;
     BlockDriverState *bs;
@@ -413,6 +413,11 @@
             params = newparams;
            format = &bdrv_raw;
         }
+       free(mode);
+       if (pasprintf(&buf, "%s/mode", bpath) == -1)
+           mode = NULL;
+       else
+           mode = xs_read(xsh, XBT_NULL, buf, &len);
 
 #if 0
        /* Phantom VBDs are disabled because the use of paths
@@ -454,6 +459,9 @@
             if (pasprintf(&buf, "%s/params", bpath) != -1)
                 xs_watch(xsh, buf, dev);
         }
+
+        if (mode && strchr(mode, 'w') == NULL)
+            bdrv_set_read_only(bs);
 
         /* open device now if media present */
 #ifdef CONFIG_STUBDOM
@@ -571,6 +579,7 @@
     }
 
  out:
+    free(mode);
     free(danger_type);
     free(params);
     free(dev);

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