Re: [Qemu-devel] [PATCH] loadvm for read-only snapshot files
On 03/02/2008, Eddie Kohler [EMAIL PROTECTED] wrote: The following patch, against cvs, supports read-only snapshots on read-only qcow2 image files. Snapshots can be loaded, but not saved. This is really useful in my context, which is operating systems projects; a read-only memory snapshot allows students to share a snapshot that skips the boot process, allowing them to run their code right away. Please let me know if anything needs changing. Instead of including block_int.h in vl.c you should use the provided functions from block.h (bs-drv can be checked with _is_inserted). -- Please do not print this email unless absolutely necessary. Spread environmental awareness.
Re: [Qemu-devel] [PATCH] loadvm for read-only snapshot files
andrzej zaborowski wrote:
On 03/02/2008, Eddie Kohler [EMAIL PROTECTED] wrote:
The following patch, against cvs, supports read-only snapshots on read-only
qcow2 image files. Snapshots can be loaded, but not saved. This is really
useful in my context, which is operating systems projects; a read-only memory
snapshot allows students to share a snapshot that skips the boot process,
allowing them to run their code right away.
Please let me know if anything needs changing.
Instead of including block_int.h in vl.c you should use the provided
functions from block.h (bs-drv can be checked with _is_inserted).
Thanks for the comment. The attached patch introduces a new block.h function,
bdev_is_snapshot_capable. Better?
Eddie
Index: block-qcow2.c
===
RCS file: /sources/qemu/qemu/block-qcow2.c,v
retrieving revision 1.10
diff -u -u -r1.10 block-qcow2.c
--- block-qcow2.c 11 Nov 2007 02:51:16 - 1.10
+++ block-qcow2.c 10 Feb 2008 23:54:34 -
@@ -429,7 +429,6 @@
BDRVQcowState *s = bs-opaque;
int new_l1_size, new_l1_size2, ret, i;
uint64_t *new_l1_table;
-uint64_t new_l1_table_offset;
uint64_t data64;
uint32_t data32;
@@ -450,28 +449,32 @@
memcpy(new_l1_table, s-l1_table, s-l1_size * sizeof(uint64_t));
/* write new table (align to cluster) */
-new_l1_table_offset = alloc_clusters(bs, new_l1_size2);
+if (!bs-read_only) {
+ uint64_t new_l1_table_offset = alloc_clusters(bs, new_l1_size2);
-for(i = 0; i s-l1_size; i++)
-new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
-ret = bdrv_pwrite(s-hd, new_l1_table_offset, new_l1_table, new_l1_size2);
-if (ret != new_l1_size2)
-goto fail;
-for(i = 0; i s-l1_size; i++)
-new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
-
-/* set new table */
-data64 = cpu_to_be64(new_l1_table_offset);
-if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_table_offset),
-data64, sizeof(data64)) != sizeof(data64))
-goto fail;
-data32 = cpu_to_be32(new_l1_size);
-if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_size),
-data32, sizeof(data32)) != sizeof(data32))
-goto fail;
+ for(i = 0; i s-l1_size; i++)
+ new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
+ ret = bdrv_pwrite(s-hd, new_l1_table_offset, new_l1_table, new_l1_size2);
+ if (ret != new_l1_size2)
+ goto fail;
+ for(i = 0; i s-l1_size; i++)
+ new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
+
+ /* set new table */
+ data64 = cpu_to_be64(new_l1_table_offset);
+ if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_table_offset),
+ data64, sizeof(data64)) != sizeof(data64))
+ goto fail;
+ data32 = cpu_to_be32(new_l1_size);
+ if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_size),
+ data32, sizeof(data32)) != sizeof(data32))
+ goto fail;
+ free_clusters(bs, s-l1_table_offset, s-l1_size * sizeof(uint64_t));
+
+ s-l1_table_offset = new_l1_table_offset;
+}
+
qemu_free(s-l1_table);
-free_clusters(bs, s-l1_table_offset, s-l1_size * sizeof(uint64_t));
-s-l1_table_offset = new_l1_table_offset;
s-l1_table = new_l1_table;
s-l1_size = new_l1_size;
return 0;
@@ -521,7 +524,8 @@
/* update the L1 entry */
s-l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;
tmp = cpu_to_be64(l2_offset | QCOW_OFLAG_COPIED);
-if (bdrv_pwrite(s-hd, s-l1_table_offset + l1_index * sizeof(tmp),
+if (!bs-read_only
+ bdrv_pwrite(s-hd, s-l1_table_offset + l1_index * sizeof(tmp),
tmp, sizeof(tmp)) != sizeof(tmp))
return 0;
min_index = l2_cache_new_entry(bs);
@@ -535,7 +539,8 @@
s-l2_size * sizeof(uint64_t))
return 0;
}
-if (bdrv_pwrite(s-hd, l2_offset,
+if (!bs-read_only
+ bdrv_pwrite(s-hd, l2_offset,
l2_table, s-l2_size * sizeof(uint64_t)) !=
s-l2_size * sizeof(uint64_t))
return 0;
@@ -624,7 +629,8 @@
}
/* update L2 table */
l2_table[l2_index] = tmp;
-if (bdrv_pwrite(s-hd,
+if (!bs-read_only
+ bdrv_pwrite(s-hd,
l2_offset + l2_index * sizeof(tmp), tmp, sizeof(tmp)) != sizeof(tmp))
return 0;
return cluster_offset;
@@ -1322,7 +1328,7 @@
}
}
}
-if (l2_modified) {
+if (l2_modified !bs-read_only) {
if (bdrv_pwrite(s-hd,
l2_offset, l2_table, l2_size) != l2_size)
goto fail;
@@ -1342,7 +1348,7 @@
}
}
}
-if (l1_modified) {
+if (l1_modified !bs-read_only) {
for(i = 0; i l1_size; i++)
cpu_to_be64s(l1_table[i]);
if (bdrv_pwrite(s-hd, l1_table_offset, l1_table,
@@ -1553,6 +1559,9 @@
int i, ret;
uint64_t *l1_table = NULL;
+if
[Qemu-devel] [PATCH] loadvm for read-only snapshot files
Hi all,
The following patch, against cvs, supports read-only snapshots on read-only
qcow2 image files. Snapshots can be loaded, but not saved. This is really
useful in my context, which is operating systems projects; a read-only memory
snapshot allows students to share a snapshot that skips the boot process,
allowing them to run their code right away.
Please let me know if anything needs changing.
Eddie Kohler
Index: block-qcow2.c
===
RCS file: /sources/qemu/qemu/block-qcow2.c,v
retrieving revision 1.10
diff -u -u -r1.10 block-qcow2.c
--- block-qcow2.c 11 Nov 2007 02:51:16 - 1.10
+++ block-qcow2.c 3 Feb 2008 18:10:07 -
@@ -429,7 +429,6 @@
BDRVQcowState *s = bs-opaque;
int new_l1_size, new_l1_size2, ret, i;
uint64_t *new_l1_table;
-uint64_t new_l1_table_offset;
uint64_t data64;
uint32_t data32;
@@ -450,28 +449,32 @@
memcpy(new_l1_table, s-l1_table, s-l1_size * sizeof(uint64_t));
/* write new table (align to cluster) */
-new_l1_table_offset = alloc_clusters(bs, new_l1_size2);
+if (!bs-read_only) {
+ uint64_t new_l1_table_offset = alloc_clusters(bs, new_l1_size2);
-for(i = 0; i s-l1_size; i++)
-new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
-ret = bdrv_pwrite(s-hd, new_l1_table_offset, new_l1_table, new_l1_size2);
-if (ret != new_l1_size2)
-goto fail;
-for(i = 0; i s-l1_size; i++)
-new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
-
-/* set new table */
-data64 = cpu_to_be64(new_l1_table_offset);
-if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_table_offset),
-data64, sizeof(data64)) != sizeof(data64))
-goto fail;
-data32 = cpu_to_be32(new_l1_size);
-if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_size),
-data32, sizeof(data32)) != sizeof(data32))
-goto fail;
+ for(i = 0; i s-l1_size; i++)
+ new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
+ ret = bdrv_pwrite(s-hd, new_l1_table_offset, new_l1_table, new_l1_size2);
+ if (ret != new_l1_size2)
+ goto fail;
+ for(i = 0; i s-l1_size; i++)
+ new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
+
+ /* set new table */
+ data64 = cpu_to_be64(new_l1_table_offset);
+ if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_table_offset),
+ data64, sizeof(data64)) != sizeof(data64))
+ goto fail;
+ data32 = cpu_to_be32(new_l1_size);
+ if (bdrv_pwrite(s-hd, offsetof(QCowHeader, l1_size),
+ data32, sizeof(data32)) != sizeof(data32))
+ goto fail;
+ free_clusters(bs, s-l1_table_offset, s-l1_size * sizeof(uint64_t));
+
+ s-l1_table_offset = new_l1_table_offset;
+}
+
qemu_free(s-l1_table);
-free_clusters(bs, s-l1_table_offset, s-l1_size * sizeof(uint64_t));
-s-l1_table_offset = new_l1_table_offset;
s-l1_table = new_l1_table;
s-l1_size = new_l1_size;
return 0;
@@ -521,7 +524,8 @@
/* update the L1 entry */
s-l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;
tmp = cpu_to_be64(l2_offset | QCOW_OFLAG_COPIED);
-if (bdrv_pwrite(s-hd, s-l1_table_offset + l1_index * sizeof(tmp),
+if (!bs-read_only
+ bdrv_pwrite(s-hd, s-l1_table_offset + l1_index * sizeof(tmp),
tmp, sizeof(tmp)) != sizeof(tmp))
return 0;
min_index = l2_cache_new_entry(bs);
@@ -535,7 +539,8 @@
s-l2_size * sizeof(uint64_t))
return 0;
}
-if (bdrv_pwrite(s-hd, l2_offset,
+if (!bs-read_only
+ bdrv_pwrite(s-hd, l2_offset,
l2_table, s-l2_size * sizeof(uint64_t)) !=
s-l2_size * sizeof(uint64_t))
return 0;
@@ -624,7 +629,8 @@
}
/* update L2 table */
l2_table[l2_index] = tmp;
-if (bdrv_pwrite(s-hd,
+if (!bs-read_only
+ bdrv_pwrite(s-hd,
l2_offset + l2_index * sizeof(tmp), tmp, sizeof(tmp)) != sizeof(tmp))
return 0;
return cluster_offset;
@@ -1322,7 +1328,7 @@
}
}
}
-if (l2_modified) {
+if (l2_modified !bs-read_only) {
if (bdrv_pwrite(s-hd,
l2_offset, l2_table, l2_size) != l2_size)
goto fail;
@@ -1342,7 +1348,7 @@
}
}
}
-if (l1_modified) {
+if (l1_modified !bs-read_only) {
for(i = 0; i l1_size; i++)
cpu_to_be64s(l1_table[i]);
if (bdrv_pwrite(s-hd, l1_table_offset, l1_table,
@@ -1553,6 +1559,9 @@
int i, ret;
uint64_t *l1_table = NULL;
+if (bs-read_only)
+ return -EACCES;
+
memset(sn, 0, sizeof(*sn));
if (sn_info-id_str[0] == '\0') {
@@ -1628,7 +1637,8 @@
return -ENOENT;
sn = s-snapshots[snapshot_index];
-if (update_snapshot_refcount(bs, s-l1_table_offset, s-l1_size, -1) 0)
+if (!bs-read_only
+
