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shellpop skeleton

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Motiejus Jakštys
2022-02-15 10:49:03 +02:00
committed by Motiejus Jakštys
parent ce882b9086
commit f584642cca
6 changed files with 222 additions and 21 deletions
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44
README.md
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@@ -66,10 +66,10 @@ consumed heap space for each separate turbonss instance will be minimal.
Tight packing places some constraints on the underlying data:
- Maximum database size: 4GB.
- Maximum length of username and groupname: 32 bytes.
- Maximum length of shell and homedir: 64 bytes.
- Maximum comment ("gecos") length: 256 bytes.
- Username and groupname must be utf8-encoded.
- Permitted length of username and groupname: 1-32 bytes.
- Permitted length of shell and homedir: 1-64 bytes.
- Permitted comment ("gecos") length: 0-255 bytes.
- Username, groupname and gecos must be utf8-encoded.
Checking out and building
-------------------------
@@ -156,7 +156,7 @@ OFFSET TYPE NAME DESCRIPTION
0 [4]u8 magic always 0xf09fa4b7
4 u8 version now `0`
5 u16 bom 0x1234
7 u8 padding
7 u6 num_shells max value: 63
8 u32 num_users number of passwd entries
12 u32 num_groups number of group entries
16 u32 offset_cmph_uid2user
@@ -165,9 +165,8 @@ OFFSET TYPE NAME DESCRIPTION
28 u32 offset_idx offset to the first idx_ section
32 u32 offset_groups
36 u32 offset_users
40 u32 offset_shells
44 u32 offset_groupmembers
48 u32 offset_additional_gids
40 u32 offset_groupmembers
44 u32 offset_additional_gids
```
`magic` is 0xf09fa4b7, and `version` must be `0`. All integers are
@@ -255,15 +254,25 @@ few examples: `/bin/bash`, `/usr/bin/nologin`, `/bin/zsh` among others.
Therefore, "shells" have an optimization: they can be pointed by in the
external list, or reside among the user's data.
64 (1>>6) most popular shells (i.e. referred to by at least two User entries)
are stored externally in "Shells" area. The less popular ones are stored with
63 most popular shells (i.e. referred to by at least two User entries) are
stored externally in "Shells" area. The less popular ones are stored with
userdata.
The `shell_here=true` bit signifies that the shell is stored with userdata.
`false` means it is stored in the `Shells` section. If the shell is stored
"here", it is the first element in `stringdata`, and it's length is
`shell_len_or_place`. If it is stored externally, the latter variable points
to it's index in the external storage.
There are two "Shells" areas: the index and the blob. The index is a list of
structs which point to a location in the "blob" area:
```
const ShellIndex = struct {
offset: u10,
len: u6,
};
```
In the user's struct the `shell_here=true` bit signifies that the shell is
stored with userdata. `false` means it is stored in the `Shells` section. If
the shell is stored "here", it is the first element in `stringdata`, and it's
length is `shell_len_or_place`. If it is stored externally, the latter variable
points to it's index in the ShellIndex area.
Shells in the external storage are sorted by their weight, which is
`length*frequency`.
@@ -315,7 +324,7 @@ Each section is padded to 64 bytes.
```
SECTION SIZE DESCRIPTION
Header 52 see "Turbonss header" section
Header 48 see "Turbonss header" section
cmph_gid2group ? gid->group cmph
cmph_uid2user ? uid->user cmph
cmph_groupname2group ? groupname->group cmph
@@ -324,9 +333,10 @@ 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
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)
Shells ? See "Shells" section
groupmembers ? per-group memberlist (32b padding)
additional_gids ? per-user grouplist (8b padding)
```