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Date: Wed, 11 Feb 2009 15:09:46 +0200
From: Andriy Gapon <avg@icyb.net.ua>
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Subject: Re: generalizing fd allocation code to id allocation
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My nose has just been rubbed into alloc_unr(9) :)
Thanks, Roman!

on 11/02/2009 14:53 Andriy Gapon said the following:
> Guys,
> 
> anybody has ideas (or code) for generalizing code in
> sys/kern/kern_descrip.c for managing fd-s ("small" integer numbers)?
> 
> I mean divorcing that code from filedesc and making it re-usable
> wherever we need some (constrained) id allocation.
> By constrained I mean that either ids are allocated from a sufficiently
> small limited pool or it is desirable to keep ids at small values.
> 
> I needed this in a small driver that I am slowly writing and here's some
> bits from it:
> 
> #define NDSLOTTYPE      uint64_t
> #define NDSLOTSIZE      sizeof(NDSLOTTYPE)
> #define NDENTRIES       (NDSLOTSIZE * __CHAR_BIT)
> #define NDSLOT(x)       ((x) / NDENTRIES)
> #define NDBIT(x)        ((NDSLOTTYPE)1 << ((x) % NDENTRIES))
> #define NDSLOTS(x)      (((x) + NDENTRIES - 1) / NDENTRIES)
> ...
> /* XXX ugly */
> NDSLOTTYPE host_addr_map[NDSLOTS(sizeof(uint8_t) * __CHAR_BIT)];
> ...
> static uint8_t alloc_host_addr(struct heci_softc *sc)
> {
>         static const int maxoff = sizeof(sc->host_addr_map) /
> sizeof(sc->host_addr_map[0]);
>         NDSLOTTYPE *map = sc->host_addr_map;
>         int off;
> 
>         for (off = 0; off < maxoff; ++off) {
>                 if (map[off] != ~0UL) {
>                         uint8_t addr = off * NDENTRIES + ffsl(~map[off])
> - 1;
>                         map[NDSLOT(addr)] |= NDBIT(addr);
>                         return (addr);
>                 }
>         }
> 
>         /* XXX what to return if all addresses are in use? */
>         /* use the fact that zero is a reserved address */
>         return 0;
> }
> 
> static void
> release_host_addr(struct heci_softc *sc, uint8_t addr)
> {
>         NDSLOTTYPE *map = sc->host_addr_map;
>         if (!(map[NDSLOT(addr)] & NDBIT(addr))) /* XXX make KASSERT? */
>                 device_printf(sc->dev, "release for unused host addr
> 0x%02x\n", addr);
>         map[NDSLOT(addr)] &= ~NDBIT(addr);
> }
> 
> 
> Essentially this is almost a copy/paste.
> 
> 


-- 
Andriy Gapon