[Libguestfs] [nbdkit PATCH 4/9] nbd: Implement NBD_CMD_CACHE passthrough

In the nbd plugin, if the remote server supports any form of caching, we should utilize that rather than nbdkit's fallback to .pread. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- plugins/nbd/nbd.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c index 821f256..71549d7 100644 --- a/plugins/nbd/nbd.c +++ b/plugins/nbd/nbd.c @@ -1151,6 +1151,14 @@ nbd_can_multi_conn (void *handle) return h->flags & NBD_FLAG_CAN_MULTI_CONN; } +static int +nbd_can_cache (void *handle) +{ + struct handle *h = handle; + + return h->flags & NBD_FLAG_SEND_CACHE; +} + static int nbd_can_extents (void *handle) { @@ -1245,6 +1253,18 @@ nbd_extents (void *handle, uint32_t count, uint64_t offset, return c < 0 ? c : nbd_reply (h, c); } +/* Cache a portion of the file. */ +static int +nbd_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags) +{ + struct handle *h = handle; + int c; + + assert (!flags); + c = nbd_request (h, 0, NBD_CMD_CACHE, offset, count); + return c < 0 ? c : nbd_reply (h, c); +} + static struct nbdkit_plugin plugin = { .name = "nbd", .longname = "nbdkit nbd plugin", @@ -1264,12 +1284,14 @@ static struct nbdkit_plugin plugin = { .can_fua = nbd_can_fua, .can_multi_conn = nbd_can_multi_conn, .can_extents = nbd_can_extents, + .can_cache = nbd_can_cache, .pread = nbd_pread, .pwrite = nbd_pwrite, .zero = nbd_zero, .flush = nbd_flush, .trim = nbd_trim, .extents = nbd_extents, + .cache = nbd_cache, .errno_is_preserved = 1, }; -- 2.20.1