Re: [Libguestfs] [Qemu-devel] [PATCH 1/5] nbd: Improve per-export flag handling in server

When creating a read-only image, we are still advertising support for TRIM and WRITE_ZEROES to the client, even though the client should not be issuing those commands. But seeing this requires looking across multiple functions: All callers to nbd_export_new() passed a single flag based solely on whether the export allows writes. Later, we then pass a constant set of flags to nbd_negotiate_options() (namely, the set of flags which we always support, at least for writable images), which is then further dynamically modified based on client requests for structured options. Finally, when processing NBD_OPT_EXPORT_NAME or NBD_OPT_EXPORT_GO we bitwise-or the original caller's flag with the runtime set of flags we've built up over several functions. Let's refactor things to instead compute a baseline of flags as soon as possible, in nbd_export_new(), and changing the signature for the callers to pass in a simpler bool rather than having to figure out flags. We can then get rid of the 'myflags' parameter to various functions, and instead refer to client for everything we need (we still have to perform a bitwise-OR during NBD_OPT_EXPORT_NAME and NBD_OPT_EXPORT_GO, but it's easier to see what is being computed). This lets us quit advertising senseless flags for read-only images, as well as making the next patch for exposing FAST_ZERO support easier to write. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- include/block/nbd.h | 2 +- blockdev-nbd.c | 3 +-- nbd/server.c | 62 +++++++++++++++++++++++++-------------------- qemu-nbd.c | 6 ++--- 4 files changed, 39 insertions(+), 34 deletions(-) diff --git a/include/block/nbd.h b/include/block/nbd.h index 991fd52a5134..2c87b42dfd48 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -326,7 +326,7 @@ typedef struct NBDClient NBDClient; NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset, uint64_t size, const char *name, const char *desc, - const char *bitmap, uint16_t nbdflags, bool shared, + const char *bitmap, bool readonly, bool shared, void (*close)(NBDExport *), bool writethrough, BlockBackend *on_eject_blk, Error **errp); void nbd_export_close(NBDExport *exp); diff --git a/blockdev-nbd.c b/blockdev-nbd.c index ecfa2ef0adb5..1cdffab4fce1 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -187,8 +187,7 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name, writable = false; } - exp = nbd_export_new(bs, 0, len, name, NULL, bitmap, - writable ? 0 : NBD_FLAG_READ_ONLY, !writable, + exp = nbd_export_new(bs, 0, len, name, NULL, bitmap, !writable, !writable, NULL, false, on_eject_blk, errp); if (!exp) { return; diff --git a/nbd/server.c b/nbd/server.c index 0fb41c6c50ea..b5577828aa44 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -423,14 +423,14 @@ static void nbd_check_meta_export(NBDClient *client) /* Send a reply to NBD_OPT_EXPORT_NAME. * Return -errno on error, 0 on success. */ -static int nbd_negotiate_handle_export_name(NBDClient *client, - uint16_t myflags, bool no_zeroes, +static int nbd_negotiate_handle_export_name(NBDClient *client, bool no_zeroes, Error **errp) { char name[NBD_MAX_NAME_SIZE + 1]; char buf[NBD_REPLY_EXPORT_NAME_SIZE] = ""; size_t len; int ret; + uint16_t myflags; /* Client sends: [20 .. xx] export name (length bytes) @@ -458,10 +458,13 @@ static int nbd_negotiate_handle_export_name(NBDClient *client, return -EINVAL; } - trace_nbd_negotiate_new_style_size_flags(client->exp->size, - client->exp->nbdflags | myflags); + myflags = client->exp->nbdflags; + if (client->structured_reply) { + myflags |= NBD_FLAG_SEND_DF; + }

+ trace_nbd_negotiate_new_style_size_flags(client->exp->size, myflags); stq_be_p(buf, client->exp->size); - stw_be_p(buf + 8, client->exp->nbdflags | myflags); + stw_be_p(buf + 8, myflags); len = no_zeroes ? 10 : sizeof(buf); ret = nbd_write(client->ioc, buf, len, errp); if (ret < 0) { @@ -526,8 +529,7 @@ static int nbd_reject_length(NBDClient *client, bool fatal, Error **errp) /* Handle NBD_OPT_INFO and NBD_OPT_GO. * Return -errno on error, 0 if ready for next option, and 1 to move * into transmission phase. */ -static int nbd_negotiate_handle_info(NBDClient *client, uint16_t myflags, - Error **errp) +static int nbd_negotiate_handle_info(NBDClient *client, Error **errp) { int rc; char name[NBD_MAX_NAME_SIZE + 1];