[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH] loadvm for read-only snapshot files
From: |
Eddie Kohler |
Subject: |
[Qemu-devel] [PATCH] loadvm for read-only snapshot files |
Date: |
Sun, 03 Feb 2008 10:09:46 -0800 |
User-agent: |
Thunderbird 2.0.0.9 (X11/20071115) |
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 -0000 1.10
+++ block-qcow2.c 3 Feb 2008 18:10:07 -0000
@@ -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 &&
+ update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, -1) < 0)
goto fail;
if (grow_l1_table(bs, sn->l1_size) < 0)
@@ -1640,14 +1650,17 @@
if (bdrv_pread(s->hd, sn->l1_table_offset,
s->l1_table, l1_size2) != l1_size2)
goto fail;
- if (bdrv_pwrite(s->hd, s->l1_table_offset,
- s->l1_table, l1_size2) != l1_size2)
+ if (bs->read_only)
+ s->l1_table_offset = sn->l1_table_offset;
+ else if (bdrv_pwrite(s->hd, s->l1_table_offset,
+ s->l1_table, l1_size2) != l1_size2)
goto fail;
for(i = 0;i < s->l1_size; i++) {
be64_to_cpus(&s->l1_table[i]);
}
- if (update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1) < 0)
+ if (!bs->read_only &&
+ update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1) < 0)
goto fail;
#ifdef DEBUG_ALLOC
@@ -1664,6 +1677,9 @@
QCowSnapshot *sn;
int snapshot_index, ret;
+ if (bs->read_only)
+ return -EACCES;
+
snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
if (snapshot_index < 0)
return -ENOENT;
@@ -1959,6 +1975,9 @@
int ret, refcount_table_index, block_index, refcount;
uint64_t data64;
+ if (bs->read_only)
+ return 2;
+
refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
if (refcount_table_index >= s->refcount_table_size) {
if (addend < 0)
Index: vl.c
===================================================================
RCS file: /sources/qemu/qemu/vl.c,v
retrieving revision 1.403
diff -u -u -r1.403 vl.c
--- vl.c 3 Feb 2008 03:45:47 -0000 1.403
+++ vl.c 3 Feb 2008 18:10:09 -0000
@@ -36,6 +36,7 @@
#include "qemu-timer.h"
#include "qemu-char.h"
#include "block.h"
+#include "block_int.h"
#include "audio/audio.h"
#include <unistd.h>
@@ -5969,7 +5970,8 @@
{
return (bs &&
!bdrv_is_removable(bs) &&
- !bdrv_is_read_only(bs));
+ bs->drv &&
+ bs->drv->bdrv_snapshot_goto);
}
/* device must be snapshots in order to have a reliable snapshot */
@@ -5977,7 +5979,8 @@
{
return (bs &&
!bdrv_is_removable(bs) &&
- !bdrv_is_read_only(bs));
+ bs->drv &&
+ bs->drv->bdrv_snapshot_goto);
}
static BlockDriverState *get_bs_snapshots(void)
- [Qemu-devel] [PATCH] loadvm for read-only snapshot files,
Eddie Kohler <=