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test and README tiny updates

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Motiejus Jakštys 2022-02-18 17:24:22 +02:00 committed by Motiejus Jakštys
parent 80ec63b6a4
commit 411fb91fd1
2 changed files with 41 additions and 36 deletions
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43
README.md
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@ -92,7 +92,10 @@ $ zig build test
Other commands will be documented as they are implemented.
This project uses [git subtrac][git-subtrac] for managing dependencies.
This project uses [git subtrac][git-subtrac] for managing dependencies. They
work just like regular submodules, except all the refs of the submodules are in
this repository. Repeat after me: all the submodules are in this repository.
So if you have a copy of this repo, dependencies will not disappear.
remarks on `id(1)`
------------------
@ -131,12 +134,12 @@ understand which operations need to be fast; in order of importance:
3. lookup groupname -> group.
4. lookup username -> user.
These indices can use perfect hashing like [cmph][cmph]: a perfect hash hashes
a list of bytes to a sequential list of integers. Perfect hashing algorithms
require some space, and take some time to calculate ("hashing duration"). I've
tested BDZ, which hashes [][]u8 to a sequential list of integers (not
preserving order) and CHM, preserves order. BDZ accepts an optional argument `3
<= b <= 10`.
These indices can use perfect hashing like [bdz from cmph][cmph]: a perfect
hash hashes a list of bytes to a sequential list of integers. Perfect hashing
algorithms require some space, and take some time to calculate ("hashing
duration"). I've tested BDZ, which hashes [][]u8 to a sequential list of
integers (not preserving order) and CHM, preserves order. BDZ accepts an
optional argument `3 <= b <= 10`.
* BDZ algorithm requires (b=3, 900KB, b=7, 338KB, b=10, 306KB) for 1M values.
* Latency to resolve 1M keys: (170ms, 180ms, 230ms, respectively).
@ -159,9 +162,9 @@ OFFSET TYPE NAME DESCRIPTION
u8 num_shells max value: 63. Padding is strange on little endian.
8 u32 num_users number of passwd entries
12 u32 num_groups number of group entries
16 u32 offset_cmph_uid2user
20 u32 offset_cmph_groupname2group
24 u32 offset_cmph_username2user
16 u32 offset_bdz_uid2user
20 u32 offset_bdz_groupname2group
24 u32 offset_bdz_username2user
28 u32 offset_idx offset to the first idx_ section
32 u32 offset_groups
36 u32 offset_users
@ -182,7 +185,7 @@ all `offset_*` values could be `u26`. As `u32` is easier to visualize with xxd,
and the header block fits to 64 bytes anyway, we are keeping them as u32 now.
Sections whose lengths can be calculated do not have a corresponding `offset_*`
header field. For example, `cmph_gid2group` comes immediately after the header,
header field. For example, `bdz_gid2group` comes immediately after the header,
and `idx_groupname2group` comes after `idx_gid2group`, whose offset is
`offset_idx`, and size can be calculated.
@ -330,14 +333,14 @@ Each section is padded to 64 bytes.
```
SECTION SIZE DESCRIPTION
Header 48 see "Turbonss header" section
cmph_gid2group ? gid->group cmph
cmph_uid2user ? uid->user cmph
cmph_groupname2group ? groupname->group cmph
cmph_username2user ? username->user cmph
idx_gid2group len(group)*4*29/32 cmph->offset gid2group
idx_groupname2group len(group)*4*29/32 cmph->offset groupname2group
idx_uid2user len(user)*4*29/32 cmph->offset uid2user
idx_username2user len(user)*4*29/32 cmph->offset username2user
bdz_gid2group ? gid->group bdz
bdz_uid2user ? uid->user bdz
bdz_groupname2group ? groupname->group bdz
bdz_username2user ? username->user bdz
idx_gid2group len(group)*4*29/32 bdz->offset gid2group
idx_groupname2group len(group)*4*29/32 bdz->offset groupname2group
idx_uid2user len(user)*4*29/32 bdz->offset uid2user
idx_username2user len(user)*4*29/32 bdz->offset username2user
ShellIndex len(shells)*2 Shell index array
ShellBlob <= 4032 Shell data blob (max 63*64 bytes)
Groups ? packed Group entries (8b padding)
@ -346,7 +349,7 @@ groupmembers ? per-group memberlist (32b padding)
additional_gids ? per-user grouplist (8b padding)
```
[git-subtrac]: https://github.com/apenwarr/git-subtrac/
[git-subtrac]: https://apenwarr.ca/log/20191109
[cmph]: http://cmph.sourceforge.net/
[id]: https://linux.die.net/man/1/id
[nsswitch]: https://linux.die.net/man/5/nsswitch.conf

34
src/header.zig
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@ -8,7 +8,7 @@ const Bom = 0x1234;
pub const SectionLength = 64;
const HeaderError = error{
const InvalidHeader = error{
InvalidMagic,
InvalidVersion,
InvalidBom,
@ -23,16 +23,16 @@ const Header = packed struct {
num_shells: u8,
num_users: u32,
num_groups: u32,
offset_cmph_uid2user: u32,
offset_cmph_groupname2group: u32,
offset_cmph_username2user: u32,
offset_bdz_uid2user: u32,
offset_bdz_groupname2group: u32,
offset_bdz_username2user: u32,
offset_idx: u32,
offset_groups: u32,
offset_users: u32,
offset_groupmembers: u32,
offset_additional_gids: u32,
pub fn init(blob: [HeaderSize]u8) HeaderError!Header {
pub fn init(blob: [HeaderSize]u8) InvalidHeader!Header {
const self = @bitCast(Header, blob);
for (Magic) |item, index| {
if (self.magic[index] != item) return error.InvalidMagic;
@ -48,9 +48,9 @@ const Header = packed struct {
}
const offsets = [_]u32{
self.offset_cmph_uid2user,
self.offset_cmph_groupname2group,
self.offset_cmph_username2user,
self.offset_bdz_uid2user,
self.offset_bdz_groupname2group,
self.offset_bdz_username2user,
self.offset_idx,
self.offset_groups,
self.offset_users,
@ -73,12 +73,15 @@ const Header = packed struct {
const testing = std.testing;
test "constants and types are reasonable" {
test "header is byte-aligned" {
try testing.expectEqual(HeaderSize * 8, @bitSizeOf(Header));
}
test "Section length is a power of two" {
try testing.expect(std.math.isPowerOfTwo(SectionLength));
}
test "header pack and unpack" {
test "header pack, unpack and validation" {
const goodHeader = Header{
.magic = Magic,
.version = Version,
@ -86,9 +89,9 @@ test "header pack and unpack" {
.num_shells = 0,
.num_users = 0,
.num_groups = 0,
.offset_cmph_uid2user = 0,
.offset_cmph_groupname2group = 0,
.offset_cmph_username2user = 0,
.offset_bdz_uid2user = 0,
.offset_bdz_groupname2group = 0,
.offset_bdz_username2user = 0,
.offset_idx = 0,
.offset_groups = 0,
.offset_users = 0,
@ -96,8 +99,7 @@ test "header pack and unpack" {
.offset_additional_gids = 0,
};
const blob = goodHeader.asArray();
const gotHeader = try Header.init(blob);
const gotHeader = try Header.init(goodHeader.asArray());
try testing.expectEqual(goodHeader, gotHeader);
{
@ -120,7 +122,7 @@ test "header pack and unpack" {
{
var header = goodHeader;
header.offset_cmph_uid2user = 65;
header.offset_bdz_uid2user = 65;
try testing.expectError(error.InvalidOffset, Header.init(header.asArray()));
}
}