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qemu-nbd: Use raw block driver for --offset
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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 <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Message-Id: <[email protected]>
Acked-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
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@kevmw
kevmw committed Oct 2, 2020
1 parent 060102a commit b57e4de
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Showing 4 changed files with 31 additions and 42 deletions.
9 changes: 1 addition & 8 deletions blockdev-nbd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -154,7 +154,6 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
BlockDriverState *bs = NULL;
BlockBackend *on_eject_blk;
NBDExport *exp = NULL;
int64_t len;
AioContext *aio_context;

assert(exp_args->type == BLOCK_EXPORT_TYPE_NBD);
Expand Down Expand Up @@ -192,12 +191,6 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)

aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
len = bdrv_getlength(bs);
if (len < 0) {
error_setg_errno(errp, -len,
"Failed to determine the NBD export's length");
goto out;
}

if (!arg->has_writable) {
arg->writable = false;
Expand All @@ -206,7 +199,7 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
arg->writable = false;
}

exp = nbd_export_new(bs, 0, len, arg->name, arg->description, arg->bitmap,
exp = nbd_export_new(bs, arg->name, arg->description, arg->bitmap,
!arg->writable, !arg->writable,
NULL, false, on_eject_blk, errp);
if (!exp) {
Expand Down
4 changes: 2 additions & 2 deletions include/block/nbd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -331,8 +331,8 @@ typedef struct NBDExport NBDExport;
typedef struct NBDClient NBDClient;

BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp);
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);
Expand Down
33 changes: 16 additions & 17 deletions nbd/server.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -1507,18 +1506,26 @@ 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)
{
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,
Expand Down Expand Up @@ -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);
Expand All @@ -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) {
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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);

Expand All @@ -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;
}
Expand All @@ -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;
}
Expand Down
27 changes: 12 additions & 15 deletions qemu-nbd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -524,7 +524,6 @@ int main(int argc, char **argv)
const char *port = NULL;
char *sockpath = NULL;
char *device = NULL;
int64_t fd_size;
QemuOpts *sn_opts = NULL;
const char *sn_id_or_name = NULL;
const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:B:L";
Expand Down Expand Up @@ -1037,6 +1036,17 @@ int main(int argc, char **argv)
}
bs = blk_bs(blk);

if (dev_offset) {
QDict *raw_opts = qdict_new();
qdict_put_str(raw_opts, "driver", "raw");
qdict_put_str(raw_opts, "file", bs->node_name);
qdict_put_int(raw_opts, "offset", dev_offset);
bs = bdrv_open(NULL, NULL, raw_opts, flags, &error_fatal);
blk_remove_bs(blk);
blk_insert_bs(blk, bs, &error_fatal);
bdrv_unref(bs);
}

blk_set_enable_write_cache(blk, !writethrough);

if (sn_opts) {
Expand All @@ -1054,21 +1064,8 @@ int main(int argc, char **argv)
}

bs->detect_zeroes = detect_zeroes;
fd_size = blk_getlength(blk);
if (fd_size < 0) {
error_report("Failed to determine the image length: %s",
strerror(-fd_size));
exit(EXIT_FAILURE);
}

if (dev_offset >= fd_size) {
error_report("Offset (%" PRIu64 ") has to be smaller than the image "
"size (%" PRId64 ")", dev_offset, fd_size);
exit(EXIT_FAILURE);
}
fd_size -= dev_offset;

export = nbd_export_new(bs, dev_offset, fd_size, export_name,
export = nbd_export_new(bs, export_name,
export_description, bitmap, readonly, shared > 1,
nbd_export_closed, writethrough, NULL,
&error_fatal);
Expand Down

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