Date: Wed, 26 Sep 2001 00:36:37 -0400 From: The Anarcat <anarcat@anarcat.dyndns.org> To: Libh <freebsd-libh@freebsd.org> Subject: libdisk doc Message-ID: <20010926003636.B499@shall.anarcat.dyndns.org>
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Hi.
I'm writing this here because I don't know where else it wouldn't be
noise. :)
I'm digging around libdisk because (correct me if I'm wrong) libhdisk is
not really documented and pretty much only a wrapper for libdisk. Now,
the only doc I could find on libdisk is the man page, and it's kinda
short on details. :)
By looking at /usr/src/release/sysinstall/label.c, I've been able to
make up a nice ascii graphic of a a Disk and Chunk hierarchy (attached).
The file also contains an procedure used in label.c to extract the info
from such a tree.
I think this grandiose work of art should be put somewhere. ;)
Seriously, I spent a while trying to figure out how this thing was
setup. In particular, I am still wondering why there is an
"intermediary" struct Chunk between the struct Disk and the head of the
slice list (see picture).
All this and more (disklabel.h FS_* macros), should be documented
somewhere (is it?).
Anyways, don't want to hit on anyones head here, and I'm probably just
too unused to libh?disk... :)
I hope the nice drawing will be useful, if not entertaining, at least.
A.
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We have the structures:
+--------+ +-------+
| Disk | | Chunk |=20
| | | | This chunk represents the disk in itself
| chunks--->| part |=20
+--------+ +--|----+=20
| =20
+--------------|---------------------------+
|Slices (e.g. | freebsd, linux, dos) |
| V |
| +-----------+ +-----------+ |
| | Chunk | | Chunk | |
| | | | | |
| | type=3Dfbsd | | type=3Dfat | |
| | | | | |
| | part next----->| part next----> ... |
| | | | | | | |
| +--|--------+ +---|-------+ |
| | ? |
+------|-----------------------------------+
|
+------|-----------------------------------+
|Partitions (eg. fs, swap) |
| V |
| +--------------+ +--------+ |
| | Chunk | | Chunk | |
| | | | | |
| | type=3Dpart | | ... | |
| | | | | |
| | next----->| next----> ... |
| | | | | |
| | subtype=3Dswap | | ... | |
| | | | | |
| +--------------+ +--------+ |
| |
+------------------------------------------+
/* All the chunks currently displayed on the screen */
static struct {
struct chunk *c;
PartType type;
} label_chunk_info[MAX_CHUNKS + 1];
/* this function flattens such a tree in a single array */
static void
record_label_chunks(Device **devs, Device *dev)
{
int i, j, p;
struct chunk *c1, *c2;
Disk *d;
j =3D p =3D 0;
/* First buzz through and pick up the FreeBSD slices */
for (i =3D 0; devs[i]; i++) {
if ((dev && devs[i] !=3D dev) || !devs[i]->enabled)
continue;
d =3D (Disk *)devs[i]->private;
if (!d->chunks)
msgFatal("No chunk list found for %s!", d->name);
/* Put the slice entries first */
for (c1 =3D d->chunks->part; c1; c1 =3D c1->next) {
if (c1->type =3D=3D freebsd) {
label_chunk_info[j].type =3D PART_SLICE;
label_chunk_info[j].c =3D c1;
++j;
}
}
}
/* Now run through again and get the FreeBSD partition entries */
for (i =3D 0; devs[i]; i++) {
if (!devs[i]->enabled)
continue;
d =3D (Disk *)devs[i]->private;
/* Then buzz through and pick up the partitions */
for (c1 =3D d->chunks->part; c1; c1 =3D c1->next) {
if (c1->type =3D=3D freebsd) {
for (c2 =3D c1->part; c2; c2 =3D c2->next) {
if (c2->type =3D=3D part) {
if (c2->subtype =3D=3D FS_SWAP)
label_chunk_info[j].type =3D PART_SWAP;
else
label_chunk_info[j].type =3D PART_FILESYSTEM;
label_chunk_info[j].c =3D c2;
++j;
}
}
}
else if (c1->type =3D=3D fat) {
label_chunk_info[j].type =3D PART_FAT;
label_chunk_info[j].c =3D c1;
++j;
}
}
}
label_chunk_info[j].c =3D NULL;
if (here >=3D j) {
here =3D j ? j - 1 : 0;
}
}
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