[Qemu-devel] [PATCH] block/vdi: Limit maximum size even futher

[Max Reitz <mreitz@redhat.com>]

The block layer read and write functions do not like requests which are
bigger than INT_MAX bytes. Since the VDI bmap is read and written in a
single operation, its size is therefore limited accordingly. This
reduces the maximum VDI image size supported by QEMU to half of what it
currently is (down to approximately 512 TB).

The VDI test 084 has to be adapted accordingly. Actually, one could
clearly see that it was broken from the "Could not open
'TEST_DIR/t.IMGFMT': Invalid argument" line for an image which was
supposed to work just fine.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
The really funny thing about this is that test 084 still fails after
this patch for me because the computer I am currently working on only
has 4G of main memory (which is exactly what VDI requires for a 512T
image). Any reviewer is therefore kindly asked to test this test
him-/herself; I will do so once I am home (and once I remember to do
it).
---
 block/vdi.c                |  6 ++++--
 tests/qemu-iotests/084     | 14 +++++++-------
 tests/qemu-iotests/084.out | 13 ++++++++-----
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/block/vdi.c b/block/vdi.c
index 19701ee..f25e4b5 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -120,8 +120,10 @@ typedef unsigned char uuid_t[16];
 
 #define VDI_IS_ALLOCATED(X) ((X) < VDI_DISCARDED)
 
-/* max blocks in image is (0xffffffff / 4) */
-#define VDI_BLOCKS_IN_IMAGE_MAX  0x3fffffff
+/* The bmap will take up VDI_BLOCKS_IN_IMAGE_MAX * sizeof(uint32_t) bytes; since
+ * the bmap is read and written in a single operation, its size needs to be
+ * limited to INT_MAX */
+#define VDI_BLOCKS_IN_IMAGE_MAX  ((unsigned)(INT_MAX / sizeof(uint32_t)))
 #define VDI_DISK_SIZE_MAX        ((uint64_t)VDI_BLOCKS_IN_IMAGE_MAX * \
                                   (uint64_t)DEFAULT_CLUSTER_SIZE)
 
diff --git a/tests/qemu-iotests/084 b/tests/qemu-iotests/084
index 2712c02..9b710e5 100755
--- a/tests/qemu-iotests/084
+++ b/tests/qemu-iotests/084
@@ -66,15 +66,15 @@ stat -c"disk image file size in bytes: %s" "${TEST_IMG}"
 
 # check for image size too large
 # poke max image size, and appropriate blocks_in_image value
-echo "Test 1: Maximum size (1024 TB):"
-poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf0\xff\xff\xff\x03\x00"
-poke_file "$TEST_IMG" "$bii_offset" "\xff\xff\xff\x3f"
+echo "Test 1: Maximum size (512 TB):"
+poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf0\xff\xff\xff\x01\x00"
+poke_file "$TEST_IMG" "$bii_offset" "\xff\xff\xff\x1f"
 _img_info
 
 echo
-echo "Test 2: Size too large (1024TB + 1)"
+echo "Test 2: Size too large (512TB + 1)"
 # This should be too large (-EINVAL):
-poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf1\xff\xff\xff\x03\x00"
+poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf1\xff\xff\xff\x01\x00"
 _img_info
 
 echo
@@ -89,9 +89,9 @@ _img_info
 
 echo
 echo "Test 4: Size valid (64M), but Blocks In Image exceeds max allowed"
-# Now check the bounds of blocks_in_image - 0x3fffffff should be the max
+# Now check the bounds of blocks_in_image - 0x1fffffff should be the max
 # value here, and we should get -ENOTSUP
-poke_file "$TEST_IMG" "$bii_offset" "\x00\x00\x00\x40"
+poke_file "$TEST_IMG" "$bii_offset" "\x00\x00\x00\x20"
 _img_info
 
 # Finally, 1MB is the only block size supported.  Verify that
diff --git a/tests/qemu-iotests/084.out b/tests/qemu-iotests/084.out
index ea29ae0..4ac0157 100644
--- a/tests/qemu-iotests/084.out
+++ b/tests/qemu-iotests/084.out
@@ -17,17 +17,20 @@ file format: IMGFMT
 virtual size: 64M (67108864 bytes)
 cluster_size: 1048576
 disk image file size in bytes: 1024
-Test 1: Maximum size (1024 TB):
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Could not open 'TEST_DIR/t.IMGFMT': Invalid argument
+Test 1: Maximum size (512 TB):
+image: TEST_DIR/t.IMGFMT
+file format: IMGFMT
+virtual size: 512T (562949952372736 bytes)
+cluster_size: 1048576
 
-Test 2: Size too large (1024TB + 1)
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Unsupported VDI image size (size is 0x3fffffff10000, max supported is 0x3fffffff00000)
+Test 2: Size too large (512TB + 1)
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Unsupported VDI image size (size is 0x1fffffff10000, max supported is 0x1fffffff00000)
 
 Test 3: Size valid (64M), but Blocks In Image too small (63)
 qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (disk size 67108864, image bitmap has room for 66060288)
 
 Test 4: Size valid (64M), but Blocks In Image exceeds max allowed
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (too many blocks 1073741824, max is 1073741823)
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (too many blocks 536870912, max is 536870911)
 
 Test 5: Valid Image: 64MB, Blocks In Image 64, Block Size 1MB
 image: TEST_DIR/t.IMGFMT
-- 
1.9.3