nbd_block_status_filter3

Usage

 #include <libnbd.h>
 typedef struct {
   int (*callback) (void *user_data,
                    const char *metacontext,
                    uint64_t offset, nbd_extent *entries,
                    size_t nr_entries, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_extent64_callback;
 int nbd_block_status_filter (
       struct nbd_handle *h, uint64_t count,
       uint64_t offset, char **contexts,
       nbd_extent64_callback extent64_callback,
       uint32_t flags
     );

Overview

Issue a filtered block status command to the NBD server. If supported by the server (see nbd_can_block_status_payload(3)), this causes metadata context information about blocks beginning from the specified offset to be returned, and with the result limited to just the contexts specified in "filter". Note that all strings in "filter" must be supported by nbd_can_meta_context(3).

All other parameters to this function have the same semantics as in nbd_block_status_64(3); except that for convenience, unless <nbd_set_strict_flags(3)> was used to disable "LIBNBD_STRICT_AUTO_FLAG", libnbd ignores the presence or absence of the flag "LIBNBD_CMD_FLAG_PAYLOAD_LEN" in "flags", while correctly using the flag over the wire.

By default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure, such as requesting an unknown command flag. The nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server reply rather than failing fast.

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", "contexts". For more information see "Non-NULL parameters" in libnbd(3).

Handle state

nbd_block_status_filter can be called when the handle is in the following state:

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

Version

This function first appeared in libnbd 1.18.

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

 #define LIBNBD_HAVE_NBD_BLOCK_STATUS_FILTER 1