[Qemu-devel] [PATCH 1/5] qcow2: Add corrupt bit

[Max Reitz <mreitz@redhat.com>]

This adds an incompatible bit indicating corruption to qcow2. Any image
with this bit set may not be written to unless for repairing (and
subsequently clearing the bit if the repair has been successful).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c              | 44 ++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.h              |  7 ++++++-
 docs/specs/qcow2.txt       |  7 ++++++-
 include/block/block.h      |  2 ++
 qemu-img.c                 |  2 +-
 tests/qemu-iotests/031.out | 12 ++++++------
 tests/qemu-iotests/036.out |  2 +-
 7 files changed, 66 insertions(+), 10 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 3376901..1d0d7ca 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -272,6 +272,37 @@ static int qcow2_mark_clean(BlockDriverState *bs)
     return 0;
 }
 
+/*
+ * Marks the image as corrupt.
+ */
+int qcow2_mark_corrupt(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+
+    s->incompatible_features |= QCOW2_INCOMPAT_CORRUPT;
+    return qcow2_update_header(bs);
+}
+
+/*
+ * Marks the image as consistent, i.e., unsets the corrupt bit, and flushes
+ * before if necessary.
+ */
+int qcow2_mark_consistent(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+
+    if (s->incompatible_features & QCOW2_INCOMPAT_CORRUPT) {
+        int ret = bdrv_flush(bs);
+        if (ret < 0) {
+            return ret;
+        }
+
+        s->incompatible_features &= ~QCOW2_INCOMPAT_CORRUPT;
+        return qcow2_update_header(bs);
+    }
+    return 0;
+}
+
 static int qcow2_check(BlockDriverState *bs, BdrvCheckResult *result,
                        BdrvCheckMode fix)
 {
@@ -402,6 +433,14 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags)
         goto fail;
     }
 
+    if (s->incompatible_features & QCOW2_INCOMPAT_CORRUPT) {
+        /* Corrupt images may not be written to unless they are being repaired */
+        if ((flags & BDRV_O_RDWR) && !(flags & BDRV_O_REPAIR)) {
+            ret = -EACCES;
+            goto fail;
+        }
+    }
+
     /* Check support for various header values */
     if (header.refcount_order != 4) {
         report_unsupported(bs, "%d bit reference counts",
@@ -1130,6 +1169,11 @@ int qcow2_update_header(BlockDriverState *bs)
             .name = "dirty bit",
         },
         {
+            .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
+            .bit  = QCOW2_INCOMPAT_CORRUPT_BITNR,
+            .name = "corrupt bit",
+        },
+        {
             .type = QCOW2_FEAT_TYPE_COMPATIBLE,
             .bit  = QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
             .name = "lazy refcounts",
diff --git a/block/qcow2.h b/block/qcow2.h
index dba9771..4297487 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -119,9 +119,12 @@ enum {
 /* Incompatible feature bits */
 enum {
     QCOW2_INCOMPAT_DIRTY_BITNR   = 0,
+    QCOW2_INCOMPAT_CORRUPT_BITNR = 1,
     QCOW2_INCOMPAT_DIRTY         = 1 << QCOW2_INCOMPAT_DIRTY_BITNR,
+    QCOW2_INCOMPAT_CORRUPT       = 1 << QCOW2_INCOMPAT_CORRUPT_BITNR,
 
-    QCOW2_INCOMPAT_MASK          = QCOW2_INCOMPAT_DIRTY,
+    QCOW2_INCOMPAT_MASK          = QCOW2_INCOMPAT_DIRTY
+                                 | QCOW2_INCOMPAT_CORRUPT,
 };
 
 /* Compatible feature bits */
@@ -361,6 +364,8 @@ int qcow2_backing_read1(BlockDriverState *bs, QEMUIOVector *qiov,
                   int64_t sector_num, int nb_sectors);
 
 int qcow2_mark_dirty(BlockDriverState *bs);
+int qcow2_mark_corrupt(BlockDriverState *bs);
+int qcow2_mark_consistent(BlockDriverState *bs);
 int qcow2_update_header(BlockDriverState *bs);
 
 /* qcow2-refcount.c functions */
diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
index 36a559d..33eca36 100644
--- a/docs/specs/qcow2.txt
+++ b/docs/specs/qcow2.txt
@@ -80,7 +80,12 @@ in the description of a field.
                                 tables to repair refcounts before accessing the
                                 image.
 
-                    Bits 1-63:  Reserved (set to 0)
+                    Bit 1:      Corrupt bit.  If this bit is set then any data
+                                structure may be corrupt and the image must not
+                                be written to (unless for regaining
+                                consistency).
+
+                    Bits 2-63:  Reserved (set to 0)
 
          80 -  87:  compatible_features
                     Bitmask of compatible features. An implementation can
diff --git a/include/block/block.h b/include/block/block.h
index 742fce5..7145bf0 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -74,6 +74,8 @@ typedef struct BlockDevOps {
 #define BDRV_O_CHECK       0x1000  /* open solely for consistency check */
 #define BDRV_O_ALLOW_RDWR  0x2000  /* allow reopen to change from r/o to r/w */
 #define BDRV_O_UNMAP       0x4000  /* execute guest UNMAP/TRIM operations */
+#define BDRV_O_REPAIR      0x8000  /* assure any writes are intended only for
+                                      repairs (important for corrupt images) */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH)
 
diff --git a/qemu-img.c b/qemu-img.c
index b9a848d..28c6376 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -558,7 +558,7 @@ static int img_check(int argc, char **argv)
             fmt = optarg;
             break;
         case 'r':
-            flags |= BDRV_O_RDWR;
+            flags |= BDRV_O_RDWR | BDRV_O_REPAIR;
 
             if (!strcmp(optarg, "leaks")) {
                 fix = BDRV_FIX_LEAKS;
diff --git a/tests/qemu-iotests/031.out b/tests/qemu-iotests/031.out
index 796c993..a943344 100644
--- a/tests/qemu-iotests/031.out
+++ b/tests/qemu-iotests/031.out
@@ -54,7 +54,7 @@ header_length             72
 
 Header extension:
 magic                     0x6803f857
-length                    96
+length                    144
 data                      <binary>
 
 Header extension:
@@ -68,7 +68,7 @@ No errors were found on the image.
 
 magic                     0x514649fb
 version                   2
-backing_file_offset       0xf8
+backing_file_offset       0x128
 backing_file_size         0x17
 cluster_bits              16
 size                      67108864
@@ -92,7 +92,7 @@ data                      'host_device'
 
 Header extension:
 magic                     0x6803f857
-length                    96
+length                    144
 data                      <binary>
 
 Header extension:
@@ -155,7 +155,7 @@ header_length             104
 
 Header extension:
 magic                     0x6803f857
-length                    96
+length                    144
 data                      <binary>
 
 Header extension:
@@ -169,7 +169,7 @@ No errors were found on the image.
 
 magic                     0x514649fb
 version                   3
-backing_file_offset       0x118
+backing_file_offset       0x148
 backing_file_size         0x17
 cluster_bits              16
 size                      67108864
@@ -193,7 +193,7 @@ data                      'host_device'
 
 Header extension:
 magic                     0x6803f857
-length                    96
+length                    144
 data                      <binary>
 
 Header extension:
diff --git a/tests/qemu-iotests/036.out b/tests/qemu-iotests/036.out
index 063ca22..55a3e6e 100644
--- a/tests/qemu-iotests/036.out
+++ b/tests/qemu-iotests/036.out
@@ -46,7 +46,7 @@ header_length             104
 
 Header extension:
 magic                     0x6803f857
-length                    96
+length                    144
 data                      <binary>
 
 *** done
-- 
1.8.3.1