nbd_trim(3)

📦
version 1.25.8 · 18 versions
, in centos-stream 10

💅 nbd_trim(3) — the libnbd girlies' guide

okay so bestie, welcome to the nbd_trim(3) manual page from LIBNBD. yes it's a C function. no you're not gonna be scared of it. let's go 🎀

✨ NAME ✨

nbd_trim — send a trim command to the NBD server. that's it, that's the vibe. you're telling the server "hey, delete this chunk for me" and the server either gets it or it doesn't 💅

🌸 SYNOPSIS 🌸

#include <libnbd.h>

int nbd_trim (
      struct nbd_handle *h, uint64_t count,
      uint64_t offset, uint32_t flags
    );

look at that signature. four args. h is your handle, count is the size, offset is where, flags is the extras. she's neat, she's tidy, she's giving main character energy 🔥

🦋 DESCRIPTION 🦋

so what actually happens: you issue a trim command to the NBD server, and if the server supports it, it punches a hole in the backing store — starting at offset and ending at offset + count - 1. like literally carving out a chunk. iconic honestly ✨

the call returns when the server has acknowledged the command, or when there's an error. not before, not after, she waits her turn 🫶

heads up bestie: this will generally return an error if nbd_can_trim(3) is false, or if nbd_is_read_only(3) is true. like duh, you can't trim a read-only thing. be so serious rn 😭

also — and this is the part everyone forgets — not all servers can support a count of 4GiB or larger. nbd_get_extended_headers_negotiated(3) is your bestie here: it tells you which servers will actually parse a request bigger than 32 bits. the NBD protocol does not yet have a way for a client to learn if the server will enforce an even smaller maximum trim size — although a future extension may add a constraint visible in nbd_get_block_size(3). so like. watch this space ✨

about flags

the flags parameter may be 0 for no flags, or it may contain LIBNBD_CMD_FLAG_FUA — which means the server shouldn't return until the data has been committed to permanent storage. but only if that is supported — some servers literally cannot do this, check nbd_can_fua(3) first, i'm begging 🙈

💖 RETURN VALUE 💖

if the call is successful, the function returns 0. slay. that's the good ending 💅

🔥 ERRORS 🔥

on error, -1 is returned. that's the not-so-girlboss ending 💀

refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error. the lore is all in there, iykyk.

also: the following parameters must not be NULL: h. do not pass NULL. i'm not asking. for more info see "Non-NULL parameters" in libnbd(3) 🫶

⭐ NOTES ⭐

Strict call

by default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure — like requesting an unknown command flag. rude? maybe. sensible? yes bestie 💖

the nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server reply rather than failing fast. so if you want to be chaotic and hear the server out, that's your girl.

👑 HANDLE STATE 👑

nbd_trim 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

so basically: connect first. there's exactly one green check and it's the one where you're actually connected. the way that every other row is just no 😭

🌈 VERSION 🌈

this function first appeared in libnbd 1.0. a legend from the beginning, no cap 👑

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

#define LIBNBD_HAVE_NBD_TRIM 1

🎀 SEE ALSO 🎀

nbd_aio_trim(3), nbd_can_fua(3), nbd_can_trim(3), nbd_create(3), nbd_get_block_size(3), nbd_get_extended_headers_negotiated(3), nbd_is_read_only(3), nbd_set_strict_mode(3), libnbd(3).

the whole friend group, fr fr 🫶

🍓 AUTHORS 🍓

  • Eric Blake
  • Richard W.M. Jones

the actual masterminds behind this. respect the architects 💜

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 bestie, you ate that 💅 this was libnbd-1.25.8, dated 2026-10-13, and she's filed under nbd_trim(3). go punch some holes in a backing store responsibly 🌸✨

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