nbd_set_request_block_size3

Usage

 #include <libnbd.h>
 int nbd_set_request_block_size (
       struct nbd_handle *h, bool request
     );

Overview

By default, when connecting to an export, libnbd requests that the server report any block size restrictions. The NBD protocol states that a server may supply block sizes regardless of whether the client requests them, and libnbd will report those block sizes (see nbd_get_block_size(3)); conversely, if a client does not request block sizes, the server may reject the connection instead of dealing with a client sending unaligned requests. This function makes it possible to test server behavior by emulating older clients.

Note that even when block size is requested, the server is not obligated to provide any. Furthermore, if block sizes are provided (whether or not the client requested them), libnbd enforces alignment to those sizes unless nbd_set_strict_mode(3) is used to bypass client-side safety checks.

Return value

If the call is successful the function returns 0.

Errors

On error -1 is returned.

Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

The following parameters must not be NULL: "h". For more information see "Non-NULL parameters" in libnbd(3).

Handle state

nbd_set_request_block_size can be called when the handle is in the following states:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ✅ allowed              │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ error                │
 └─────────────────────────────────────┴─────────────────────────┘

Version

This function first appeared in libnbd 1.12.

If you need to test if this function is available at compile time check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_SET_REQUEST_BLOCK_SIZE 1