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-rw-r--r--block.c17
-rw-r--r--block/vvfat.c1
-rw-r--r--blockdev.c2
-rw-r--r--include/block/block.h2
-rw-r--r--qapi/block-core.json7
5 files changed, 28 insertions, 1 deletions
diff --git a/block.c b/block.c
index 3132c78f01..96090c3b9a 100644
--- a/block.c
+++ b/block.c
@@ -930,6 +930,7 @@ static void bdrv_inherited_options(int *child_flags, QDict *child_options,
/* Inherit the read-only option from the parent if it's not set */
qdict_copy_default(child_options, parent_options, BDRV_OPT_READ_ONLY);
+ qdict_copy_default(child_options, parent_options, BDRV_OPT_AUTO_READ_ONLY);
/* Our block drivers take care to send flushes and respect unmap policy,
* so we can default to enable both on lower layers regardless of the
@@ -1053,6 +1054,7 @@ static void bdrv_backing_options(int *child_flags, QDict *child_options,
/* backing files always opened read-only */
qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "on");
+ qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "off");
flags &= ~BDRV_O_COPY_ON_READ;
/* snapshot=on is handled on the top layer */
@@ -1142,6 +1144,10 @@ static void update_flags_from_options(int *flags, QemuOpts *opts)
*flags |= BDRV_O_RDWR;
}
+ assert(qemu_opt_find(opts, BDRV_OPT_AUTO_READ_ONLY));
+ if (qemu_opt_get_bool_del(opts, BDRV_OPT_AUTO_READ_ONLY, false)) {
+ *flags |= BDRV_O_AUTO_RDONLY;
+ }
}
static void update_options_from_flags(QDict *options, int flags)
@@ -1156,6 +1162,10 @@ static void update_options_from_flags(QDict *options, int flags)
if (!qdict_haskey(options, BDRV_OPT_READ_ONLY)) {
qdict_put_bool(options, BDRV_OPT_READ_ONLY, !(flags & BDRV_O_RDWR));
}
+ if (!qdict_haskey(options, BDRV_OPT_AUTO_READ_ONLY)) {
+ qdict_put_bool(options, BDRV_OPT_AUTO_READ_ONLY,
+ flags & BDRV_O_AUTO_RDONLY);
+ }
}
static void bdrv_assign_node_name(BlockDriverState *bs,
@@ -1329,6 +1339,11 @@ QemuOptsList bdrv_runtime_opts = {
.help = "Node is opened in read-only mode",
},
{
+ .name = BDRV_OPT_AUTO_READ_ONLY,
+ .type = QEMU_OPT_BOOL,
+ .help = "Node can become read-only if opening read-write fails",
+ },
+ {
.name = "detect-zeroes",
.type = QEMU_OPT_STRING,
.help = "try to optimize zero writes (off, on, unmap)",
@@ -2486,6 +2501,8 @@ BlockDriverState *bdrv_open_blockdev_ref(BlockdevRef *ref, Error **errp)
qdict_set_default_str(qdict, BDRV_OPT_CACHE_DIRECT, "off");
qdict_set_default_str(qdict, BDRV_OPT_CACHE_NO_FLUSH, "off");
qdict_set_default_str(qdict, BDRV_OPT_READ_ONLY, "off");
+ qdict_set_default_str(qdict, BDRV_OPT_AUTO_READ_ONLY, "off");
+
}
bs = bdrv_open_inherit(NULL, reference, qdict, 0, NULL, NULL, errp);
diff --git a/block/vvfat.c b/block/vvfat.c
index f2e7d501cf..98ba5e2bac 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -3130,6 +3130,7 @@ static void vvfat_qcow_options(int *child_flags, QDict *child_options,
int parent_flags, QDict *parent_options)
{
qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "off");
+ qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "off");
qdict_set_default_str(child_options, BDRV_OPT_CACHE_NO_FLUSH, "on");
}
diff --git a/blockdev.c b/blockdev.c
index c30495d035..fc8794862f 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2651,7 +2651,7 @@ void qmp_blockdev_change_medium(bool has_device, const char *device,
bdrv_flags = blk_get_open_flags_from_root_state(blk);
bdrv_flags &= ~(BDRV_O_TEMPORARY | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING |
- BDRV_O_PROTOCOL);
+ BDRV_O_PROTOCOL | BDRV_O_AUTO_RDONLY);
if (!has_read_only) {
read_only = BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN;
diff --git a/include/block/block.h b/include/block/block.h
index b189cf422e..580b3716c3 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -115,6 +115,7 @@ typedef struct HDGeometry {
select an appropriate protocol driver,
ignoring the format layer */
#define BDRV_O_NO_IO 0x10000 /* don't initialize for I/O */
+#define BDRV_O_AUTO_RDONLY 0x20000 /* degrade to read-only if opening read-write fails */
#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)
@@ -125,6 +126,7 @@ typedef struct HDGeometry {
#define BDRV_OPT_CACHE_DIRECT "cache.direct"
#define BDRV_OPT_CACHE_NO_FLUSH "cache.no-flush"
#define BDRV_OPT_READ_ONLY "read-only"
+#define BDRV_OPT_AUTO_READ_ONLY "auto-read-only"
#define BDRV_OPT_DISCARD "discard"
#define BDRV_OPT_FORCE_SHARE "force-share"
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0fc1590c1b..d4fe710836 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3656,6 +3656,12 @@
# either generally or in certain configurations. In this case,
# the default value does not work and the option must be
# specified explicitly.
+# @auto-read-only: if true and @read-only is false, QEMU may automatically
+# decide not to open the image read-write as requested, but
+# fall back to read-only instead (and switch between the modes
+# later), e.g. depending on whether the image file is writable
+# or whether a writing user is attached to the node
+# (default: false, since 3.1)
# @detect-zeroes: detect and optimize zero writes (Since 2.1)
# (default: off)
# @force-share: force share all permission on added nodes.
@@ -3671,6 +3677,7 @@
'*discard': 'BlockdevDiscardOptions',
'*cache': 'BlockdevCacheOptions',
'*read-only': 'bool',
+ '*auto-read-only': 'bool',
'*force-share': 'bool',
'*detect-zeroes': 'BlockdevDetectZeroesOptions' },
'discriminator': 'driver',