Re: [Qemu-devel] [PATCH v2 resend 3/4] Block: readonly changes
Am 04.02.2010 23:04, schrieb Naphtali Sprei:
> Open backing file for read-only
> During commit upgrade to read-write and back at end to read-only
>
> Signed-off-by: Naphtali Sprei
> ---
> block.c | 68
> ---
> block_int.h |1 +
> 2 files changed, 61 insertions(+), 8 deletions(-)
>
> diff --git a/block.c b/block.c
> index 66564de..4a9df91 100644
> --- a/block.c
> +++ b/block.c
> @@ -451,7 +451,6 @@ int bdrv_open2(BlockDriverState *bs, const char
> *filename, int flags,
> if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
> bs->enable_write_cache = 1;
>
> -bs->read_only = (flags & BDRV_O_RDWR) == 0;
> if (!(flags & BDRV_O_FILE)) {
> open_flags = (flags & (BDRV_O_RDWR |
> BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
> if (bs->is_temporary) { /* snapshot should be writeable */
> @@ -466,6 +465,7 @@ int bdrv_open2(BlockDriverState *bs, const char
> *filename, int flags,
> goto free_and_fail;
> }
>
> +bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
> if (drv->bdrv_getlength) {
> bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
> }
> @@ -482,13 +482,28 @@ int bdrv_open2(BlockDriverState *bs, const char
> *filename, int flags,
> filename, bs->backing_file);
> if (bs->backing_format[0] != '\0')
> back_drv = bdrv_find_format(bs->backing_format);
> +
> +open_flags &= ~BDRV_O_RDWR; /* clear RW, then restore from orig */
> +if (bs->is_temporary) {
> +open_flags |= (flags & BDRV_O_RDWR);
> +}
> +
> ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
> back_drv);
> -bs->backing_hd->read_only = (open_flags & BDRV_O_RDWR) == 0;
> +if (ret < 0) {
> +open_flags &= ~BDRV_O_RDWR; /* Fall-back to read-only for the
> backing file */
> +ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
> + back_drv);
> +}
Why is this needed? The only case in which a backing file is opened
read-write is during commit, right? For commit there is certainly no use
in opening it read-only instead.
This whole code looks like there are cases where a backing file is still
opened read-write by default, though the commit message says that no
such backing files exist. Am I missing something?
> if (ret < 0) {
> bdrv_close(bs);
> return ret;
> }
> +if (!bs->is_temporary) {
> +bs->backing_hd->keep_read_only = bs->keep_read_only; /* base
> image inherits from "parent" and open read-only */
This looks like more than 80 characters on a line.
What would helps here and also would improve consistency in style is to
move the comments to the line before instead of sticking them at the end
of a code line. This is true even more if the comment actually applies
to a whole block and not only to the line in which it is written (you're
doing this in other places).
> +} else {
> +bs->backing_hd->keep_read_only = !(flags & BDRV_O_RDWR);
> +}
> }
>
> if (!bdrv_key_required(bs)) {
> @@ -564,19 +579,38 @@ int bdrv_commit(BlockDriverState *bs)
> {
> BlockDriver *drv = bs->drv;
> int64_t i, total_sectors;
> -int n, j;
> +int n, j, ro, open_flags;
> int ret = 0;
> unsigned char sector[512];
> +char filename[1024];
> +BlockDriverState *bs_rw, *bs_ro;
>
> if (!drv)
> return -ENOMEDIUM;
> +
> +if (!bs->backing_hd) {
> + return -ENOTSUP;
> +}
>
> -if (bs->read_only) {
> +if (bs->backing_hd->keep_read_only) {
> return -EACCES;
> }
> +
> +ro = bs->backing_hd->read_only;
> +strncpy(filename, bs->backing_hd->filename, sizeof(filename));
> +open_flags = bs->backing_hd->open_flags;
>
> -if (!bs->backing_hd) {
> - return -ENOTSUP;
> +if (ro) { /* re-open as RW */
> +bdrv_close(bs->backing_hd);
> +qemu_free(bs->backing_hd);
bdrv_delete is doing what you mean here. But actually, you don't need to
delete it, you can just reuse the old bs for re-opening the image.
> +
> +bs_rw = bdrv_new("");
> +ret = bdrv_open2(bs_rw, filename, open_flags | BDRV_O_RDWR, NULL);
> +if (ret < 0) {
> +bdrv_delete(bs_rw);
> +return -EACCES;
Why don't you pass the right return value up? Apart from that, you
should re-open the backing file (read-only) or the VM will get into
trouble...
> +}
> +bs->backing_hd = bs_rw;
Eek... ;-) Well, it should work, as far as I know the block drivers.
> }
>
> total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
> @@ -584,11 +618,13 @@ int bdrv_commit(BlockDriverState *bs)
> if (drv->bdrv_is_allocated(bs, i, 65536, &n)) {
> for(j = 0; j < n; j++
[Qemu-devel] [PATCH v2 resend 3/4] Block: readonly changes
Open backing file for read-only
During commit upgrade to read-write and back at end to read-only
Signed-off-by: Naphtali Sprei
---
block.c | 68 ---
block_int.h |1 +
2 files changed, 61 insertions(+), 8 deletions(-)
diff --git a/block.c b/block.c
index 66564de..4a9df91 100644
--- a/block.c
+++ b/block.c
@@ -451,7 +451,6 @@ int bdrv_open2(BlockDriverState *bs, const char *filename,
int flags,
if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
bs->enable_write_cache = 1;
-bs->read_only = (flags & BDRV_O_RDWR) == 0;
if (!(flags & BDRV_O_FILE)) {
open_flags = (flags & (BDRV_O_RDWR |
BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
if (bs->is_temporary) { /* snapshot should be writeable */
@@ -466,6 +465,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename,
int flags,
goto free_and_fail;
}
+bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
if (drv->bdrv_getlength) {
bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
}
@@ -482,13 +482,28 @@ int bdrv_open2(BlockDriverState *bs, const char
*filename, int flags,
filename, bs->backing_file);
if (bs->backing_format[0] != '\0')
back_drv = bdrv_find_format(bs->backing_format);
+
+open_flags &= ~BDRV_O_RDWR; /* clear RW, then restore from orig */
+if (bs->is_temporary) {
+open_flags |= (flags & BDRV_O_RDWR);
+}
+
ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
back_drv);
-bs->backing_hd->read_only = (open_flags & BDRV_O_RDWR) == 0;
+if (ret < 0) {
+open_flags &= ~BDRV_O_RDWR; /* Fall-back to read-only for the
backing file */
+ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
+ back_drv);
+}
if (ret < 0) {
bdrv_close(bs);
return ret;
}
+if (!bs->is_temporary) {
+bs->backing_hd->keep_read_only = bs->keep_read_only; /* base image
inherits from "parent" and open read-only */
+} else {
+bs->backing_hd->keep_read_only = !(flags & BDRV_O_RDWR);
+}
}
if (!bdrv_key_required(bs)) {
@@ -564,19 +579,38 @@ int bdrv_commit(BlockDriverState *bs)
{
BlockDriver *drv = bs->drv;
int64_t i, total_sectors;
-int n, j;
+int n, j, ro, open_flags;
int ret = 0;
unsigned char sector[512];
+char filename[1024];
+BlockDriverState *bs_rw, *bs_ro;
if (!drv)
return -ENOMEDIUM;
+
+if (!bs->backing_hd) {
+ return -ENOTSUP;
+}
-if (bs->read_only) {
+if (bs->backing_hd->keep_read_only) {
return -EACCES;
}
+
+ro = bs->backing_hd->read_only;
+strncpy(filename, bs->backing_hd->filename, sizeof(filename));
+open_flags = bs->backing_hd->open_flags;
-if (!bs->backing_hd) {
- return -ENOTSUP;
+if (ro) { /* re-open as RW */
+bdrv_close(bs->backing_hd);
+qemu_free(bs->backing_hd);
+
+bs_rw = bdrv_new("");
+ret = bdrv_open2(bs_rw, filename, open_flags | BDRV_O_RDWR, NULL);
+if (ret < 0) {
+bdrv_delete(bs_rw);
+return -EACCES;
+}
+bs->backing_hd = bs_rw;
}
total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
@@ -584,11 +618,13 @@ int bdrv_commit(BlockDriverState *bs)
if (drv->bdrv_is_allocated(bs, i, 65536, &n)) {
for(j = 0; j < n; j++) {
if (bdrv_read(bs, i, sector, 1) != 0) {
-return -EIO;
+ret = -EIO;
+goto ro_cleanup;
}
if (bdrv_write(bs->backing_hd, i, sector, 1) != 0) {
-return -EIO;
+ret = -EIO;
+goto ro_cleanup;
}
i++;
}
@@ -608,6 +644,22 @@ int bdrv_commit(BlockDriverState *bs)
*/
if (bs->backing_hd)
bdrv_flush(bs->backing_hd);
+
+ro_cleanup:
+
+if (ro) { /* re-open as RO */
+bdrv_close(bs->backing_hd);
+qemu_free(bs->backing_hd);
+bs_ro = bdrv_new("");
+ret = bdrv_open2(bs_ro, filename, open_flags & ~BDRV_O_RDWR, NULL);
+if (ret < 0) {
+bdrv_delete(bs_ro);
+return -EACCES;
+}
+bs->backing_hd = bs_ro;
+bs->backing_hd->keep_read_only = 0;
+}
+
return ret;
}
diff --git a/block_int.h b/block_int.h
index 9144d37..02fae5b 100644
--- a/block_int.h
+++ b/block_int.h
@@ -130,6 +130,7 @@ struct BlockDriverState {
int64_t total_sectors; /* if we are reading a disk image, give its
size in sectors */
int read_only; /* if true, the media is read only */
+int keep_read_only; /* if true, the media wa
