DECLARE_GEOM_CLASS(9)

okay bestie, welcome to DECLARE_GEOM_CLASS(9), and yes it’s from the Kernel Developer's Manual — we’re doing kernel macro lore today 💅✨

🌸 NAME 🌸

DECLARE_GEOM_CLASS — the GEOM class declaration macro, aka the official little doorway for registering your GEOM class 🫶

✨ SYNOPSIS ✨

#include <geom/geom.h>

DECLARE_GEOM_CLASS(class, mod_name);

💖 DESCRIPTION 💖

okay so the DECLARE_GEOM_CLASS() macro registers a GEOM class in GEOM. A GEOM class itself implements one particular kind of transformation — think of it as a class with main character energy that does exactly one transformation job. Typical examples are: MBR disk partition, BSD disklabel and RAID5 classes. DECLARE_GEOM_CLASS() can be used both for compiled in and loaded as kld(4) modules GEOM classes, and it is the only official way for class registration. periodt 🔥

The arguments to DECLARE_GEOM_CLASS() are:

• class — The g_class structure which describes a GEOM class.
• mod_name — A kernel module name (not a class name!) 👀

Structure g_class contains data describing the class. They are:

• const char * name — Class name.
• g_taste_t * taste — Pointer to function used for taste event handling. If it is non-NULL it is called in three situations:
  • On class activation, all existing providers are offered for tasting.
  • When new provider is created it is offered for tasting.
  • After last write access to a provider is closed it is offered for retasting (on first write open event “spoil” was sent).
• g_config_t * config — This field is not used anymore, its functionality was replaced by the ctlreq field. 🫠
• g_ctl_req_t * ctlreq — Pointer to function used for handling events from userland applications.
• g_init_t * init — Pointer to function which is called right after class registration.
• g_fini_t * fini — Pointer to function which is called right before class deregistration.
• g_ctl_destroy_geom_t * destroy_geom — Pointer to a function which is called for every geom on class unload. If this field is not set, the class can not be unloaded. 😭

Only a name field is required; the rest are optional. slay, minimal setup 💅

🚧 RESTRICTIONS/CONDITIONS 🚧

The fields of g_class should always be initialized using C99-style field naming (see the initialization of example_class below). no chaotic free-for-all field assignment, bestie 🎀

🦋 EXAMPLES 🦋

Example class declaration.

static struct g_geom *
g_example_taste(struct g_class *mp, struct g_provider *pp,
    int flags __unused)
{
        g_topology_assert();

        [...]
}

static void
g_example_ctlreq(struct gctl_req *req, struct g_class *cp,
    char const *verb)
{

        [...]
}

static int
g_example_destroy_geom(struct gctl_req *req, struct g_class *cp,
    struct g_geom *gp)
{

        g_topology_assert();

        [...]
}

static void
g_example_init(struct g_class *mp)
{

        [...]
}

static void
g_example_fini(struct g_class *mp)
{

        [...]
}

struct g_class example_class = {
        .name = "EXAMPLE",
        .taste = g_example_taste,
        .ctlreq = g_example_ctlreq,
        .init = g_example_init,
        .fini = g_example_fini,
        .destroy_geom = g_example_destroy_geom
};

DECLARE_GEOM_CLASS(example_class, g_example);

🌈 SEE ALSO 🌈

geom(4), g_attach(9), g_bio(9), g_consumer(9), g_data(9), g_event(9), g_geom(9), g_provider(9), g_provider_by_name(9), g_wither_geom(9)

👑 AUTHORS 👑

This manual page was written by Pawel Jakub Dawidek <pjd@FreeBSD.org>. iconic behavior, fr fr 🫶

---

xoxo, this page came from Debian, dated August 13, 2007 — DECLARE_GEOM_CLASS(9) signing off with sparkles 🎀✨