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Razor Design

The corner stone of razor is the package set on-disk data structure / file format. It is how razor represents the packages installed on the system and it's what razor downloads from upstream servers to find out what's available. It's a simple binary file format, somewhat inspired by the ELF binary format. It has a sorted list of all packages and a sorted list of all unique properties (requires/provides/conflicts/obsoletes). Each package has a list of the properties associated with it (a list of indices into the list of all properties) and each property has a list of packages that it belongs to (as a list of indices into the package list). Strings are stored in a string pool, and referred to by their byte index in the pool.

Much of this is still changing, but as of June 13th, this write up from Dan Winship is reasonably accurate. The repo file format / razor_set data structure starts with a header, containing some number of sections, terminated by a section with type 0:

struct razor_set_header {
        uint32_t magic;
        uint32_t version;
        struct razor_set_section sections[0];

struct razor_set_section {
        uint32_t type;
        uint32_t offset;
        uint32_t size;

razor_set_open() mmaps the repo file, and creates a struct razor_set:

struct razor_set {
        struct array string_pool;
        struct array packages;
        struct array properties;
        struct array files;
        struct array package_pool;
        struct array property_pool;
        struct array file_pool;
        struct razor_set_header *header;

by finding the sections with those IDs and creating "struct array"s pointing to the right places in the mmap()ed data. (This is the only processing needed when reading in the file; everything else is used exactly as-is.) The sections

Data types

Note that the exact layout of bits involves some historical accidents. (Particularly the fact that the "name" field in most structs loses its high bits to a flags field.)

struct list_head {
        uint list_ptr : 24;
        uint flags    : 8;

struct list {
        uint data  : 24;
        uint flags : 8;

Used to store lists of package, property, or file IDs. "struct list_head" stores the head of the list, which points to one or more "struct list"s in the appropriate "pool" section. ("struct list" should probably be called "struct list_item".)