nbd_aio_block_status_filter(3)

📦
version 1.25.8 · 16 versions
, in centos-stream 10

💅 nbd_aio_block_status_filter(3) — bestie's guide to pinging the NBD server for a filtered block status

okay so this whole page lives in LIBNBD (that's the library these manpages belong to, iykyk) and it's honestly giving "send a message and don't wait for the reply" energy. the function is literally called nbd_aio_block_status_filter and it does exactly what it says on the tin: fires off a filtered block status command to the NBD server, asynchronously, like a queen who refuses to block. 👑

✨ NAME ✨

nbd_aio_block_status_filter — send filtered block status command to the NBD server 💌

🌸 SYNOPSIS 🌸

here's the whole cast of characters, no cap:

#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;

typedef struct {
  int (*callback) (void *user_data, int *error);
  void *user_data;
  void (*free) (void *user_data);
} nbd_completion_callback;

int64_t nbd_aio_block_status_filter (
          struct nbd_handle *h, uint64_t count,
          uint64_t offset, char **contexts,
          nbd_extent64_callback extent64_callback,
          nbd_completion_callback completion_callback,
          uint32_t flags
        );

yes bestie that's a lot of parameters. it's giving "group project where everyone has a job." 🫶

🦋 DESCRIPTION 🦋

so. you're sending a filtered block status command to the NBD server. that's the whole thing. the filtered part is doing heavy lifting here — the plain version is a different function, and this one is the glow-up.

to check if the command actually completed, you call nbd_aio_command_completed(3). that's your vibe check. ✅

or — and this is the iconique option — you supply the optional completion_callback, which gets invoked exactly as described in "Completion callbacks" in libnbd(3). so no polling, no anxiety, the callback just shows up when it's ready. main character energy fr fr.

💫 small but important: all the other parameters behave as documented in nbd_block_status_filter(3). not making this up, not adding anything, that's just where the lore lives. go read that page if you need the deets.

🎀 RETURN VALUE 🎀

this call hands you back the 64 bit cookie of the command. 🍪

  • the cookie is ≥ 1
  • cookies are unique — but lowkey only per libnbd handle, not globally. so don't go thinking your cookie is special across the whole universe, it's special to your handle. 🙈

💀 ERRORS 💀

on error, -1 is returned. that's it. that's the whole number.

for how to get further details of the error (because -1 alone is not it, bestie), refer to "ERROR HANDLING" in libnbd(3).

⚠️ real talk: the following parameters must not be NULL: "h", "contexts". for more info see "Non-NULL parameters" in libnbd(3). do not test her with a NULL, she will not be cute about it.

🔥 NOTES 🔥

Strict call

by default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure — like, say, requesting an unknown command flag. it's giving protective best friend. 🛡️

the nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server reply rather than failing fast. so like, you can change the rules, but that's a choice you're making. 💅

👑 HANDLE STATE 👑

nbd_aio_block_status_filter can be called when the handle is in the following state. this is the whole vibe chart, study it:

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

so yeah — connected to the server is the only ✅. everything else is a no. one door, and it's the "Connected to the server" door. 🚪✨

🌈 VERSION 🌈

this function first appeared in libnbd 1.18. she's not a legacy icon, she's a relatively recent icon.

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

#define LIBNBD_HAVE_NBD_AIO_BLOCK_STATUS_FILTER 1

#ifdef her and you're golden. 🧚

🍓 SEE ALSO 🍓

the whole friend group, in order:

💜 AUTHORS 💜

Eric Blake

Richard W.M. Jones

legends, both of them. 🫶

Copyright Red Hat

🌸 LICENSE 🌸

this library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

this library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. see the GNU Lesser General Public License for more details.

you should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

okay that's the whole page, you ate that. 💅✨ this beauty is from libnbd-1.25.8, dated 2026-10-13, and it's nbd_aio_block_status_filter(3) forever and always. go forth and filter those block statuses, bestie 🦋🎀

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