Re: [Libguestfs] [nbdkit PATCH 6/9] server: Cache per-connection can_FOO flags

Similar to the previous patch in caching size, we want to avoid calling into the plugin more than once per connection on any of the flag determination callbacks.

+++ b/server/protocol-handshake.c @@ -51,87 +51,72 @@ protocol_compute_eflags (struct connection *conn, uint16_t *flags) { uint16_t eflags = NBD_FLAG_HAS_FLAGS; int fl; + bool can_write = true; fl = backend_can_write (backend, conn); if (fl == -1) return -1; if (readonly || !fl) { eflags |= NBD_FLAG_READ_ONLY; - conn->readonly = true; + can_write = false;

+++ b/server/protocol.c @@ -64,14 +64,19 @@ validate_request (struct connection *conn, uint16_t cmd, uint16_t flags, uint64_t offset, uint32_t count, uint32_t *error) { + int r; + /* Readonly connection? */ - if (conn->readonly && - (cmd == NBD_CMD_WRITE || cmd == NBD_CMD_TRIM || - cmd == NBD_CMD_WRITE_ZEROES)) { - nbdkit_error ("invalid request: %s: write request on readonly connection", - name_of_nbd_cmd (cmd)); - *error = EROFS; - return false; + if (cmd == NBD_CMD_WRITE || cmd == NBD_CMD_TRIM || + cmd == NBD_CMD_WRITE_ZEROES) { + r = backend_can_write (backend, conn);