Date: Wed, 26 Sep 2001 13:03:50 -0400 From: The Anarcat <anarcat@anarcat.dyndns.org> To: freebsd-doc@freebsd.org Cc: freebsd-hackers@freebsd.org Subject: libh?disk doc (deficiencies?) Message-ID: <20010926130350.C40172@shall.anarcat.dyndns.org>
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[crossposted to -hackers in a hope to have more information, sorry if
this is inappropriate]
Hi.
I'm currently working a bit on libh, which includes a libhdisk library
to interface libdisk(3), newfs, etc, in short, a interface to operate
disk partition/slice edition =E0 la sysinstall.
The thing is that I'm trying to figure out how all this stuff works.
libdisk(3) is not very informative, in fact, it doesn't document
anything below the "slice" level (FS_SWAP macro and structure of a
Disk/Chunk tree, for example).
I made a little graphic (ASCII!) to show how such a tree (Disk/Chunk) is
made, along with an algorithm from sysinstall's label.c that extract
relevant data out of it.
I will make documentation for the Disk/Chunk class hierarchy and
functions, and that will imply investigating libdisk's functions.=20
I think libdisk(3) should be split and rewrote. Anyways, isn't it policy
to have *functions* instead of *libraries* documented in manpages? :)
The thing is that I might not be the best person to do it, and I do not
understand everything clearly yet. If anyone has any other source of
information (apart from source code), please share. :) I will probably
end up posting prs about libdisk's doc...
One thing I haven't figured out yet is why there is an intermediate
"Chunk" between Disk and slices (see picture, the first chunk on the
right of the Disk box).
I think the graphic is quite good, and should be included somewhere, for
reference because it took me a while to figure it out.
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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