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[Qemu-devel] [PULL 20/42] block/dmg: properly detect the UDIF trailer
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PULL 20/42] block/dmg: properly detect the UDIF trailer |
Date: |
Fri, 6 Feb 2015 17:40:27 +0100 |
From: Peter Wu <address@hidden>
DMG files have a variable length with a UDIF trailer at the end of a
file. This UDIF trailer is essential as it describes the contents of
the image. At the moment however, the start of this trailer is almost
always incorrect as bdrv_getlength() returns a multiple of the block
size (rounded up). This results in a failure to recognize DMG files,
resulting in Invalid argument (EINVAL) errors.
As there is no API to retrieve the real file size, look for the magic
header in the last two sectors to find the start of this 512-byte UDIF
trailer (the "koly" block).
The resource fork offset ("info_begin") has its offset adjusted as the
initial value of offset does not mean "end of file" anymore, but "begin
of UDIF trailer".
[Replaced error_set(errp, ERROR_CLASS_GENERIC_ERROR, ...) with
error_setg(errp, ...) as discussed with Peter.
--Stefan]
Signed-off-by: Peter Wu <address@hidden>
Reviewed-by: John Snow <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
Message-id: address@hidden
Signed-off-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
block/dmg.c | 47 +++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 43 insertions(+), 4 deletions(-)
diff --git a/block/dmg.c b/block/dmg.c
index e455886..cdad28f 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -131,6 +131,46 @@ static void update_max_chunk_size(BDRVDMGState *s,
uint32_t chunk,
}
}
+static int64_t dmg_find_koly_offset(BlockDriverState *file_bs, Error **errp)
+{
+ int64_t length;
+ int64_t offset = 0;
+ uint8_t buffer[515];
+ int i, ret;
+
+ /* bdrv_getlength returns a multiple of block size (512), rounded up. Since
+ * dmg images can have odd sizes, try to look for the "koly" magic which
+ * marks the begin of the UDIF trailer (512 bytes). This magic can be found
+ * in the last 511 bytes of the second-last sector or the first 4 bytes of
+ * the last sector (search space: 515 bytes) */
+ length = bdrv_getlength(file_bs);
+ if (length < 0) {
+ error_setg_errno(errp, -length,
+ "Failed to get file size while reading UDIF trailer");
+ return length;
+ } else if (length < 512) {
+ error_setg(errp, "dmg file must be at least 512 bytes long");
+ return -EINVAL;
+ }
+ if (length > 511 + 512) {
+ offset = length - 511 - 512;
+ }
+ length = length < 515 ? length : 515;
+ ret = bdrv_pread(file_bs, offset, buffer, length);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Failed while reading UDIF trailer");
+ return ret;
+ }
+ for (i = 0; i < length - 3; i++) {
+ if (buffer[i] == 'k' && buffer[i+1] == 'o' &&
+ buffer[i+2] == 'l' && buffer[i+3] == 'y') {
+ return offset + i;
+ }
+ }
+ error_setg(errp, "Could not locate UDIF trailer in dmg file");
+ return -EINVAL;
+}
+
static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
@@ -145,15 +185,14 @@ static int dmg_open(BlockDriverState *bs, QDict *options,
int flags,
s->n_chunks = 0;
s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
- /* read offset of info blocks */
- offset = bdrv_getlength(bs->file);
+ /* locate the UDIF trailer */
+ offset = dmg_find_koly_offset(bs->file, errp);
if (offset < 0) {
ret = offset;
goto fail;
}
- offset -= 0x1d8;
- ret = read_uint64(bs, offset, &info_begin);
+ ret = read_uint64(bs, offset + 0x28, &info_begin);
if (ret < 0) {
goto fail;
} else if (info_begin == 0) {
--
1.8.3.1
- [Qemu-devel] [PULL 06/42] block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes, (continued)
- [Qemu-devel] [PULL 06/42] block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 09/42] block: change default for discard and write zeroes to INT_MAX, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 08/42] block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fallocate(0) to write zeroes, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 13/42] hw/virtio-blk: add a constant for max number of merged requests, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 11/42] qed: Really remove unused field QEDAIOCB.finished, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 12/42] block: add accounting for merged requests, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 14/42] block-backend: expose bs->bl.max_transfer_length, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 17/42] qemu-iotests: Fix supported_oses check, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 15/42] virtio-blk: introduce multiread, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 18/42] iotests: Specify format for qemu-nbd, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 20/42] block/dmg: properly detect the UDIF trailer,
Kevin Wolf <=
- [Qemu-devel] [PULL 16/42] virtio-blk: add a knob to disable request merging, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 22/42] block/dmg: extract processing of resource forks, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 25/42] block/dmg: process XML plists, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 19/42] block: add event when disk usage exceeds threshold, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 26/42] block/dmg: set virtual size to a non-zero value, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 21/42] block/dmg: extract mish block decoding functionality, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 29/42] block/dmg: factor out block type check, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 24/42] block/dmg: validate chunk size to avoid overflow, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 23/42] block/dmg: process a buffer instead of reading ints, Kevin Wolf, 2015/02/06
- [Qemu-devel] [PULL 27/42] block/dmg: fix sector data offset calculation, Kevin Wolf, 2015/02/06