block: Evaluate @exact in protocol drivers

We have two protocol drivers that return success when trying to shrink a
block device even though they cannot shrink it.  This behavior is now
only allowed with exact=false, so they should return an error with
exact=true.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190918095144.955-6-mreitz@redhat.com
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/block/file-posix.c b/block/file-posix.c
index a3e8a8aa70..e0ea1a7446 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2033,6 +2033,7 @@ static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
     }
 
     if (S_ISREG(st.st_mode)) {
+        /* Always resizes to the exact @offset */
         return raw_regular_truncate(bs, s->fd, offset, prealloc, errp);
     }
 
@@ -2043,7 +2044,12 @@ static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
     }
 
     if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
-        if (offset > raw_getlength(bs)) {
+        int64_t cur_length = raw_getlength(bs);
+
+        if (offset != cur_length && exact) {
+            error_setg(errp, "Cannot resize device files");
+            return -ENOTSUP;
+        } else if (offset > cur_length) {
             error_setg(errp, "Cannot grow device files");
             return -EINVAL;
         }