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qemu-nbd: Use raw block driver for --offset

Browse source 
Instead of implementing qemu-nbd --offset in the NBD code, just put a
raw block node with the requested offset on top of the user image and
rely on that doing the job.

This does not only simplify the nbd_export_new() interface and bring it
closer to the set of options that the nbd-server-add QMP command offers,
but in fact it also eliminates a potential source for bugs in the NBD
code which previously had to add the offset manually in all relevant
places.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-7-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2020-09-24 17:26:52 +02:00
parent 060102ad65
commit b57e4de079
4 changed files with 31 additions and 42 deletions
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33
nbd/server.c
View file

@ -89,7 +89,6 @@ struct NBDExport {
BlockBackend *blk;
char *name;
char *description;
uint64_t dev_offset;
uint64_t size;
uint16_t nbdflags;
QTAILQ_HEAD(, NBDClient) clients;
@ -1507,8 +1506,8 @@ static void nbd_eject_notifier(Notifier *n, void *data)
aio_context_release(aio_context);
}
NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
uint64_t size, const char *name, const char *desc,
NBDExport *nbd_export_new(BlockDriverState *bs,
const char *name, const char *desc,
const char *bitmap, bool readonly, bool shared,
void (*close)(NBDExport *), bool writethrough,
BlockBackend *on_eject_blk, Error **errp)
@ -1516,9 +1515,17 @@ NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
AioContext *ctx;
BlockBackend *blk;
NBDExport *exp;
int64_t size;
uint64_t perm;
int ret;
size = bdrv_getlength(bs);
if (size < 0) {
error_setg_errno(errp, -size,
"Failed to determine the NBD export's length");
return NULL;
}
exp = g_new0(NBDExport, 1);
exp->common = (BlockExport) {
.drv = &blk_exp_nbd,
@ -1553,8 +1560,6 @@ NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
exp->refcount = 1;
QTAILQ_INIT(&exp->clients);
exp->blk = blk;
assert(dev_offset <= INT64_MAX);
exp->dev_offset = dev_offset;
exp->name = g_strdup(name);
assert(!desc || strlen(desc) <= NBD_MAX_STRING_SIZE);
exp->description = g_strdup(desc);
@ -1569,7 +1574,6 @@ NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
exp->nbdflags |= (NBD_FLAG_SEND_TRIM | NBD_FLAG_SEND_WRITE_ZEROES |
NBD_FLAG_SEND_FAST_ZERO);
}
assert(size <= INT64_MAX - dev_offset);
exp->size = QEMU_ALIGN_DOWN(size, BDRV_SECTOR_SIZE);
if (bitmap) {
@ -1928,8 +1932,7 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
stl_be_p(&chunk.length, pnum);
ret = nbd_co_send_iov(client, iov, 1, errp);
} else {
ret = blk_pread(exp->blk, offset + progress + exp->dev_offset,
data + progress, pnum);
ret = blk_pread(exp->blk, offset + progress, data + progress, pnum);
if (ret < 0) {
error_setg_errno(errp, -ret, "reading from file failed");
break;
@ -2303,8 +2306,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
data, request->len, errp);
}
ret = blk_pread(exp->blk, request->from + exp->dev_offset, data,
request->len);
ret = blk_pread(exp->blk, request->from, data, request->len);
if (ret < 0) {
return nbd_send_generic_reply(client, request->handle, ret,
"reading from file failed", errp);
@ -2339,7 +2341,7 @@ static coroutine_fn int nbd_do_cmd_cache(NBDClient *client, NBDRequest *request,
assert(request->type == NBD_CMD_CACHE);
ret = blk_co_preadv(exp->blk, request->from + exp->dev_offset, request->len,
ret = blk_co_preadv(exp->blk, request->from, request->len,
NULL, BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);
return nbd_send_generic_reply(client, request->handle, ret,
@ -2370,8 +2372,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
if (request->flags & NBD_CMD_FLAG_FUA) {
flags |= BDRV_REQ_FUA;
}
ret = blk_pwrite(exp->blk, request->from + exp->dev_offset,
data, request->len, flags);
ret = blk_pwrite(exp->blk, request->from, data, request->len, flags);
return nbd_send_generic_reply(client, request->handle, ret,
"writing to file failed", errp);
@ -2392,8 +2393,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
int align = client->check_align ?: 1;
int len = MIN(request->len, QEMU_ALIGN_DOWN(BDRV_REQUEST_MAX_BYTES,
align));
ret = blk_pwrite_zeroes(exp->blk, request->from + exp->dev_offset,
len, flags);
ret = blk_pwrite_zeroes(exp->blk, request->from, len, flags);
request->len -= len;
request->from += len;
}
@ -2416,8 +2416,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
int align = client->check_align ?: 1;
int len = MIN(request->len, QEMU_ALIGN_DOWN(BDRV_REQUEST_MAX_BYTES,
align));
ret = blk_co_pdiscard(exp->blk, request->from + exp->dev_offset,
len);
ret = blk_co_pdiscard(exp->blk, request->from, len);
request->len -= len;
request->from += len;
}