[Libguestfs] [PATCH nbdkit 2/4] partition: Support MBR logical partitions.
Richard W.M. Jones
rjones at redhat.com
Sun Jan 20 20:57:06 UTC 2019
---
filters/partition/nbdkit-partition-filter.pod | 5 -
filters/partition/partition-mbr.c | 108 ++++++++++++++++--
tests/test-partitioning1.sh | 22 +++-
3 files changed, 117 insertions(+), 18 deletions(-)
diff --git a/filters/partition/nbdkit-partition-filter.pod b/filters/partition/nbdkit-partition-filter.pod
index 4a615b6..ccd1b52 100644
--- a/filters/partition/nbdkit-partition-filter.pod
+++ b/filters/partition/nbdkit-partition-filter.pod
@@ -19,11 +19,6 @@ This works like the C<qemu-nbd -P> option.
The opposite of this filter is L<nbdkit-partitioning-plugin(1)> which
adds a virtual partition table to a file or files.
-=head1 NOTE
-
-Only MBR primary partitions and GPT partition tables are supported.
-MBR logical partitions are B<not> supported.
-
=head1 PARAMETERS
=over 4
diff --git a/filters/partition/partition-mbr.c b/filters/partition/partition-mbr.c
index f679db0..8e61128 100644
--- a/filters/partition/partition-mbr.c
+++ b/filters/partition/partition-mbr.c
@@ -36,14 +36,20 @@
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
+#include <inttypes.h>
#include <string.h>
+#include <errno.h>
#include <nbdkit-filter.h>
#include "byte-swapping.h"
+#include "isaligned.h"
#include "partition.h"
+/* See also linux.git/block/partitions/msdos.c:is_extended_partition */
+#define is_extended(byte) ((byte) == 0x5 || (byte) == 0xf || (byte) == 0x85)
+
struct mbr_partition {
uint8_t part_type_byte;
uint32_t start_sector;
@@ -69,20 +75,98 @@ find_mbr_partition (struct nbdkit_next_ops *next_ops, void *nxdata,
{
int i;
struct mbr_partition partition;
+ uint32_t ep_start_sector, ep_nr_sectors;
+ uint64_t ebr, next_ebr;
+ uint8_t sector[512];
- if (partnum > 4) {
- nbdkit_error ("MBR logical partitions are not supported");
+ if (partnum <= 4) { /* Primary partition. */
+ for (i = 0; i < 4; ++i) {
+ get_mbr_partition (mbr, i, &partition);
+ if (partition.nr_sectors > 0 &&
+ partition.part_type_byte != 0 &&
+ !is_extended (partition.part_type_byte) &&
+ partnum == i+1) {
+ *offset_r = partition.start_sector * 512;
+ *range_r = partition.nr_sectors * 512;
+ return 0;
+ }
+ }
+ }
+ else { /* Logical partition. */
+ /* Find the extended partition. */
+ for (i = 0; i < 4; ++i) {
+ get_mbr_partition (mbr, i, &partition);
+ if (partition.nr_sectors > 0 &&
+ is_extended (partition.part_type_byte)) {
+ goto found_extended;
+ }
+ }
+ nbdkit_error ("MBR logical partition %d (>= 5) selected, but there is no extended partition in the partition table",
+ partnum);
return -1;
- }
-
- for (i = 0; i < 4; ++i) {
- get_mbr_partition (mbr, i, &partition);
- if (partition.nr_sectors > 0 &&
- partition.part_type_byte != 0 &&
- partnum == i+1) {
- *offset_r = partition.start_sector * 512;
- *range_r = partition.nr_sectors * 512;
- return 0;
+
+ found_extended:
+ ep_start_sector = partition.start_sector;
+ ep_nr_sectors = partition.nr_sectors;
+ ebr = ep_start_sector * UINT64_C(512);
+
+ /* This loop will terminate eventually because we only accept
+ * links which strictly increase the EBR pointer.
+ */
+ for (i = 5; ; ++i) {
+ /* Read the EBR sector. */
+ if (next_ops->pread (nxdata, sector, sizeof sector, ebr, 0,
+ &errno) == -1)
+ return -1;
+
+ if (i == partnum) {
+ uint64_t offset, range;
+
+ /* First entry in EBR points to the logical partition. */
+ get_mbr_partition (sector, 0, &partition);
+
+ /* The first entry start sector is relative to the EBR. */
+ offset = ebr + partition.start_sector * UINT64_C(512);
+ range = partition.nr_sectors * UINT64_C(512);
+
+ /* Logical partition cannot be before the corresponding EBR,
+ * and it cannot extend beyond the enclosing extended
+ * partition.
+ */
+ if (offset <= ebr ||
+ offset + range >
+ ((uint64_t)ep_start_sector + ep_nr_sectors) * 512) {
+ nbdkit_error ("logical partition start or size out of range "
+ "(offset=%" PRIu64 ", range=%" PRIu64 ", "
+ "ep:startsect=%" PRIu32 ", ep:nrsects=%" PRIu32 ")",
+ offset, range, ep_start_sector, ep_nr_sectors);
+ return -1;
+ }
+ *offset_r = offset;
+ *range_r = range;
+ return 0;
+ }
+
+ /* Second entry in EBR links to the next EBR. */
+ get_mbr_partition (sector, 1, &partition);
+
+ /* All zeroes means the end of the chain. */
+ if (partition.start_sector == 0 && partition.nr_sectors == 0)
+ break;
+
+ /* The second entry start sector is relative to the start to the
+ * extended partition.
+ */
+ next_ebr = ((uint64_t)ep_start_sector + partition.start_sector) * 512;
+
+ /* Make sure the next EBR > current EBR. */
+ if (next_ebr <= ebr) {
+ nbdkit_error ("invalid EBR chain: "
+ "next EBR %" PRIu64 " <= current EBR %" PRIu64,
+ next_ebr, ebr);
+ return -1;
+ }
+ ebr = next_ebr;
}
}
diff --git a/tests/test-partitioning1.sh b/tests/test-partitioning1.sh
index 76ab43b..8aa45b9 100755
--- a/tests/test-partitioning1.sh
+++ b/tests/test-partitioning1.sh
@@ -77,7 +77,27 @@ nbdkit -f -v -D partitioning.regions=1 -U - \
# Contents of partitioning1.out should be identical to file-data.
cmp file-data partitioning1.out
-# Same test with GPT and more partitions.
+# Same test with > 4 MBR partitions.
+# Note we select partition 6 because partition 4 is the extended partition.
+nbdkit -f -v -D partitioning.regions=1 -U - \
+ --filter=partition \
+ partitioning \
+ partitioning1-p1 \
+ partitioning1-p2 \
+ partitioning1-p3 \
+ partitioning1-p4 \
+ type-guid=A2A0D0EB-E5B9-3344-87C0-68B6B72699C7 \
+ file-data \
+ type-guid=AF3DC60F-8384-7247-8E79-3D69D8477DE4 \
+ partitioning1-p5 \
+ partitioning1-p6 \
+ partition-type=mbr \
+ partition=6 \
+ --run 'qemu-img convert $nbd partitioning1.out'
+
+cmp file-data partitioning1.out
+
+# Same test with GPT.
nbdkit -f -v -D partitioning.regions=1 -U - \
--filter=partition \
partitioning \
--
2.20.1
More information about the Libguestfs
mailing list