remove 3 bytes from PackedUser
additional_gids will be stored separately.
This commit is contained in:
Motiejus Jakštys
parent
78dc63669d
commit
e06cac38b2
25
README.md
25
README.md
@ -130,7 +130,7 @@ Now that we've sketched the implementation of `id(3)`, it's clearer to
|
||||
understand which operations need to be fast; in order of importance:
|
||||
|
||||
1. lookup gid -> group info (this is on hot path in id) without members.
|
||||
2. lookup username -> user's group memberships.
|
||||
2. lookup username -> user's groups.
|
||||
3. lookup uid -> user.
|
||||
4. lookup groupname -> group.
|
||||
5. lookup username -> user.
|
||||
@ -325,7 +325,7 @@ pseudo-code:
|
||||
```
|
||||
const PackedList = struct {
|
||||
length: varint,
|
||||
members: [length]varint
|
||||
members: [length]varint,
|
||||
}
|
||||
const Groupmembers = PackedList;
|
||||
const AdditionalGids = PackedList;
|
||||
@ -333,13 +333,17 @@ const AdditionalGids = PackedList;
|
||||
|
||||
A packed list is a list of varints.
|
||||
|
||||
Section `AdditionalGidsIndex` stores an index from `hash(username)` to `offset`
|
||||
in AdditionalGids.
|
||||
|
||||
Complete file structure
|
||||
-----------------------
|
||||
|
||||
`idx_*` sections are of type `[]PackedIntArray(u29)` and are pointing to the
|
||||
respective `Groups` and `Users` entries (from the beginning of the respective
|
||||
section). Since User and Group records are 8-byte aligned, 3 bits are saved
|
||||
from every element.
|
||||
section). Since User and Group records are 8-byte aligned, 3 bits can be saved
|
||||
from every element. However, since the header easily fits to 64 bytes, we are
|
||||
storing plain `u32` for easier inspection.
|
||||
|
||||
Each section is padded to 64 bytes.
|
||||
|
||||
@ -350,16 +354,17 @@ bdz_gid2group ? gid->group bdz
|
||||
bdz_uid2user ? uid->user bdz
|
||||
bdz_groupname2group ? groupname->group bdz
|
||||
bdz_name2user ? 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_name2user len(user)*4*29/32 bdz->offset name2user
|
||||
idx_gid2group len(group)*32 bdz->offset gid2group
|
||||
idx_groupname2group len(group)*32 bdz->offset groupname2group
|
||||
idx_uid2user len(user)*32 bdz->offset uid2user
|
||||
idx_name2user len(user)*32 bdz->offset name2user
|
||||
idx_username2gids len(user)*32 Per-user gidlist index
|
||||
ShellIndex len(shells)*2 Shell index array
|
||||
ShellBlob <= 4032 Shell data blob (max 63*64 bytes)
|
||||
Groups ? packed Group entries (8b padding)
|
||||
Users ? packed User entries (8b padding)
|
||||
groupmembers ? per-group memberlist (32b padding)
|
||||
additional_gids ? per-user grouplist (8b padding)
|
||||
Groupmembers ? per-group memberlist (32b padding)
|
||||
AdditionalGids ? Per-user gidlist entries
|
||||
```
|
||||
|
||||
[git-subtrac]: https://apenwarr.ca/log/20191109
|
||||
|
||||
25
src/user.zig
25
src/user.zig
@ -9,13 +9,13 @@ const cast = std.math.cast;
|
||||
pub const PackedUser = packed struct {
|
||||
uid: u32,
|
||||
gid: u32,
|
||||
additional_gids_offset: u29,
|
||||
shell_here: bool,
|
||||
shell_len_or_idx: u6,
|
||||
home_len: u6,
|
||||
name_is_a_suffix: bool,
|
||||
name_len: u5,
|
||||
gecos_len: u8,
|
||||
padding: u5,
|
||||
|
||||
// blobSize returns the length of the blob storing string values.
|
||||
pub fn blobLength(self: *const PackedUser) usize {
|
||||
@ -93,13 +93,13 @@ pub const UserWriter = struct {
|
||||
var puser = PackedUser{
|
||||
.uid = user.uid,
|
||||
.gid = user.gid,
|
||||
.additional_gids_offset = std.math.maxInt(u29), // needs second pass
|
||||
.shell_here = self.shellIndexFn(user.shell) == null,
|
||||
.shell_len_or_idx = self.shellIndexFn(user.shell) orelse shell_len,
|
||||
.home_len = home_len,
|
||||
.name_is_a_suffix = std.mem.endsWith(u8, user.home, user.name),
|
||||
.name_len = name_len,
|
||||
.gecos_len = gecos_len,
|
||||
.padding = 0,
|
||||
};
|
||||
|
||||
try self.appendTo.appendSlice(std.mem.asBytes(&puser));
|
||||
@ -144,12 +144,10 @@ pub const UserReader = struct {
|
||||
if (it.index == it.ur.blob.len) return null;
|
||||
assert(it.index < it.ur.blob.len);
|
||||
|
||||
// https://github.com/ziglang/zig/issues/1095
|
||||
const packedUserSizeHere = @sizeOf(PackedUser);
|
||||
const endUser = it.index + packedUserSizeHere;
|
||||
const endUser = it.index + @sizeOf(PackedUser);
|
||||
var packedUser = std.mem.bytesAsValue(
|
||||
PackedUser,
|
||||
it.ur.blob[it.index..endUser][0..packedUserSizeHere],
|
||||
it.ur.blob[it.index..endUser][0..@sizeOf(PackedUser)],
|
||||
);
|
||||
const startBlob = endUser;
|
||||
const endBlob = startBlob + packedUser.blobLength();
|
||||
@ -217,19 +215,8 @@ pub const UserReader = struct {
|
||||
|
||||
const testing = std.testing;
|
||||
|
||||
test "PackedUser alignment" {
|
||||
// byte-aligned
|
||||
try testing.expectEqual(0, @rem(@bitSizeOf(PackedUser), 8));
|
||||
|
||||
const bytes = @divExact(@bitSizeOf(PackedUser), 8);
|
||||
|
||||
// External padding (PackedUserAlignmentBits) must be higher or equal to
|
||||
// the "internal" PackedUser alignment. By aligning PackedUser we are also
|
||||
// working around https://github.com/ziglang/zig/issues/10958 ; PackedUser
|
||||
// cannot be converted from/to [@bitSizeOf(PackedUser)/8]u8;
|
||||
// asBytes/bytesAsValue use @sizeOf, which is larger. Now we are putting no
|
||||
// more than 1, but it probably could be higher.
|
||||
try testing.expect(@sizeOf(PackedUser) - bytes <= 1);
|
||||
test "PackedUser internal and external alignment" {
|
||||
try testing.expectEqual(@bitSizeOf(PackedUser), @sizeOf(PackedUser) * 8);
|
||||
}
|
||||
|
||||
fn testShellIndex(shell: []const u8) ?u6 {
|
||||
|
||||
Loading…
Reference in New Issue
Block a user