X-Git-Url: https://git.saurik.com/apt.git/blobdiff_plain/17caf1b19355813fa7a58828d4979ecf21b1e1f9..860ff9593b6d706136518693b2a82db6b769e17e:/doc/cache.sgml?ds=sidebyside diff --git a/doc/cache.sgml b/doc/cache.sgml index 2e80838fa..e257dcd81 100644 --- a/doc/cache.sgml +++ b/doc/cache.sgml @@ -1,10 +1,10 @@ - + APT Cache File Format Jason Gunthorpe jgg@debian.org -$Id: cache.sgml,v 1.6 1999/02/01 02:22:11 jgg Exp $ +$Id: cache.sgml,v 1.11 2003/02/12 15:05:44 doogie Exp $ This document describes the complete implementation and format of the APT @@ -28,7 +28,7 @@ option) any later version.

For more details, on Debian GNU/Linux systems, see the file -/usr/doc/copyright/GPL for the full license. +/usr/share/common-licenses/GPL for the full license. @@ -53,10 +53,10 @@ contained in the status file which might be considered a separate package file.

-Please understand, this is designed as a -CACHE FILE- it is not ment to be -used on any system other than the one it was created for. It is not ment to -be authoritative either, ie if a system crash or software failure occures it -must be perfectly acceptable for the cache file to be in an inconsistant +Please understand, this is designed as a -CACHE FILE- it is not meant to be +used on any system other than the one it was created for. It is not meant to +be authoritative either, i.e. if a system crash or software failure occurs it +must be perfectly acceptable for the cache file to be in an inconsistent state. Furthermore at any time the cache file may be erased without losing any information. @@ -67,7 +67,7 @@ to extend it with associate cache files that contain other information.

To keep memory use down the cache file only contains often used fields and -fields that are inexepensive to store, the Package file has a full list of +fields that are inexpensive to store, the Package file has a full list of fields. Also the client may assume that all items are perfectly valid and need not perform checks against their correctness. Removal of information from the cache is possible, but blanks will be left in the file, and @@ -84,7 +84,7 @@ go through a fixup stage to get a real memory pointer. This is done by taking the index, multiplying it by the type size and then adding it to the start address of the memory block. This sounds complex, but in C it is a single array dereference. Because all items are aligned to -their size and indexs are stored as multiples of the size of the structure +their size and indexes are stored as multiples of the size of the structure the format is immediately portable to all possible architectures - BUT the generated files are -NOT-. @@ -140,11 +140,13 @@ This is the first item in the file. unsigned long VersionCount; unsigned long DependsCount; unsigned long PackageFileCount; - unsigned long MaxVerFileSize; // Offsets unsigned long FileList; // PackageFile unsigned long StringList; // StringItem + unsigned long VerSysName; // StringTable + unsigned long Architecture; // StringTable + unsigned long MaxVerFileSize; // Allocation pools struct @@ -155,7 +157,7 @@ This is the first item in the file. } Pools[7]; // Package name lookup - unsigned long HashTable[512]; // Package + unsigned long HashTable[2*1024]; // Package }; @@ -181,7 +183,7 @@ be erased and rebuilt if it is true. VerFileSz ProvidesSz *Sz contains the sizeof() that particular structure. It is used as an -extra consistancy check on the structure of the file. +extra consistency check on the structure of the file. If any of the size values do not exactly match what the client expects then the client should refuse the load the file. @@ -190,17 +192,23 @@ the client should refuse the load the file. VersionCount DependsCount PackageFileCount -These indicate the number of each structure contianed in the cache. -PackageCount is especially usefull for generating user state structures. +These indicate the number of each structure contained in the cache. +PackageCount is especially useful for generating user state structures. See Package::Id for more info. +VerSysName +String representing the version system used for this cache + +Architecture +Architecture the cache was built against. + MaxVerFileSize The maximum size of a raw entry from the original Package file -(ie VerFile::Size) is stored here. +(i.e. VerFile::Size) is stored here. FileList This contains the index of the first PackageFile structure. The PackageFile -structures are singely linked lists that represent all package files that +structures are singly linked lists that represent all package files that have been merged into the cache. StringList @@ -232,9 +240,9 @@ function:

By iterating over each entry in the hash table it is possible to iterate over -the entire list of packages. Hash Collisions are handled with a singely linked +the entire list of packages. Hash Collisions are handled with a singly linked list of packages based at the hash item. The linked list contains only -packages that macth the hashing function. +packages that match the hashing function. @@ -242,7 +250,7 @@ packages that macth the hashing function. Package

-This contians information for a single unique package. There can be any +This contains information for a single unique package. There can be any number of versions of a given package. Package exists in a singly linked list of package records starting at the hash index of the name in the Header->HashTable. @@ -252,9 +260,7 @@ the Header->HashTable. // Pointers unsigned long Name; // Stringtable unsigned long VersionList; // Version - unsigned long TargetVer; // Version unsigned long CurrentVer; // Version - unsigned long TargetDist; // StringTable (StringItem) unsigned long Section; // StringTable (StringItem) // Linked lists @@ -278,25 +284,18 @@ the Header->HashTable. Name of the package. VersionList -Base of a singely linked list of version structures. Each structure +Base of a singly linked list of version structures. Each structure represents a unique version of the package. The version structures contain links into PackageFile and the original text file as well as -detailed infromation about the size and dependencies of the specific +detailed information about the size and dependencies of the specific package. In this way multiple versions of a package can be cleanly handled -by the system. Furthermore, this linked list is guarenteed to be sorted +by the system. Furthermore, this linked list is guaranteed to be sorted from Highest version to lowest version with no duplicate entries. -TargetVer CurrentVer -This is an index (pointer) to the sub version that is being targeted for -upgrading. CurrentVer is an index to the installed version, either can be +CurrentVer is an index to the installed version, either can be 0. -TargetDist -This indicates the target distribution. Automatic upgrades should not go -outside of the specified dist. If it is 0 then the global target dist should -be used. The string should be contained in the StringItem list. - Section This indicates the deduced section. It should be "Unknown" or the section of the last parsed item. @@ -314,14 +313,14 @@ This is a linked list of all provides for this package name. SelectedState InstState CurrentState -These corrispond to the 3 items in the Status field found in the status +These correspond to the 3 items in the Status field found in the status file. See the section on defines for the possible values.

SelectedState is the state that the user wishes the package to be in.

InstState is the installation state of the package. This normally -should be Ok, but if the installation had an accident it may be otherwise. +should be OK, but if the installation had an accident it may be otherwise.

CurrentState indicates if the package is installed, partially installed or not installed. @@ -334,7 +333,7 @@ status file emitter uses this to track which packages have been emitted already. Flags -Flags are some usefull indicators of the package's state. +Flags are some useful indicators of the package's state. @@ -343,7 +342,7 @@ Flags are some usefull indicators of the package's state. PackageFile

-This contians information for a single package file. Package files are +This contains information for a single package file. Package files are referenced by Version structures. This is a singly linked list based from Header.FileList @@ -357,6 +356,8 @@ Header.FileList unsigned long Origin; // Stringtable unsigned long Label; // Stringtable unsigned long Architecture; // Stringtable + unsigned long Site; // Stringtable + unsigned long IndexType; // Stringtable unsigned long Size; // Linked list @@ -381,6 +382,12 @@ Refers the the physical disk file that this PacakgeFile represents. This is the release information. Please see the files document for a description of what the release information means. +Site +The site the index file was fetched from. + +IndexType +A string indicating what sort of index file this is. + Size Size is provided as a simple check to ensure that the package file has not been altered. @@ -401,8 +408,8 @@ Modification time for the file at time of cache generation. Version

-This contians the information for a single version of a package. This is a -singley linked list based from Package.Versionlist. +This contains the information for a single version of a package. This is a +single linked list based from Package.Versionlist.

The version list is always sorted from highest version to lowest version by @@ -425,6 +432,7 @@ VerStr). unsigned long Size; unsigned long InstalledSize; + unsigned long Hash; unsigned short ID; unsigned char Priority; }; @@ -462,9 +470,13 @@ Head of the linked list of Provides::NextPkgProv, forward provides. Size InstalledSize -The archive size for this version. For debian this is the size of the .deb +The archive size for this version. For Debian this is the size of the .deb file. Installed size is the uncompressed size for this version +Hash +This is a characteristic value representing this package. No two packages +in existence should have the same VerStr and Hash with different contents. + ID See Package::ID. @@ -480,7 +492,7 @@ This is the parsed priority value of the package. Dependency contains the information for a single dependency record. The records are split up like this to ease processing by the client. The base of list linked list is Version.DependsList. All forms of dependencies are recorded -here including Conflicts, Suggests and Recommends. +here including Conflicts, Breaks, Suggests and Recommends.

Multiple depends on the same package must be grouped together in @@ -617,7 +629,7 @@ this version. StringItem

StringItem is used for generating single instances of strings. Some things -like Section Name are are usefull to have as unique tags. It is part of +like Section Name are are useful to have as unique tags. It is part of a linked list based at Header::StringList. struct StringItem @@ -659,6 +671,7 @@ of them. #define pkgDEP_Recommends 4 #define pkgDEP_Conflicts 5 #define pkgDEP_Replaces 6 +#define pkgDEP_Breaks 8 @@ -763,7 +776,7 @@ allows the specification of a specific version and a target distribution.

Different section names on different versions is supported, but I -do not expect to use it. To simplify the GUI it will mearly use the section +do not expect to use it. To simplify the GUI it will merely use the section in the Package structure. This should be okay as I hope sections do not change much. @@ -802,7 +815,7 @@ information. (/var/cache/apt, FHS2)

Caching of the info/*.list is an excellent place to start, by generating all the list files into a tree structure and reverse linking them to the package -structures in the main cache file major speed gains in dpkg might be achived. +structures in the main cache file major speed gains in dpkg might be achieved.