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author | 2008-04-24 19:44:08 +0100 | |
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committer | 2008-04-24 19:44:08 +0100 | |
commit | c29a277be3eec6b4dd3afee0d71697dd6e07f209 (patch) | |
tree | e65bbf86229066c37c09d9a8c35c9a5f27506979 /merge.tex | |
parent | Merge branch 'historical-curiosities' (diff) | |
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Document the merge process, take 2
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diff --git a/merge.tex b/merge.tex new file mode 100644 index 0000000..b2ba786 --- /dev/null +++ b/merge.tex @@ -0,0 +1,118 @@ +\chapter{Merging and Unmerging} + +\note{In this chapter, \e{file} and \e{regular file} have their Unix meanings.} + +\section{Overview} + +The merge process merges the contents of the \t{D} directory onto the filesystem under \t{ROOT}. +This is not a straight copy; there are various subtleties which must be addressed. + +The unmerge process removes an installed package's files. It is not covered in detail in this +specification. + +\section{Directories} + +Directories are merged recursively onto the filesystem. The method used to perform the merge is not +specified, so long as the end result is correct. In particular, merging a directory may alter or +remove the source directory under \t{D}. + +Ebuilds must not attempt to merge a directory on top of any existing file that is not either a +directory or a symlink to a directory. + +\subsection{Permissions} + +The owner, group and mode (including set*id and sticky bits) of the directory must be preserved, +except as follows: + +\begin{compactitem} +\item Any directory owned by the user used to perform the build must become owned by the root user. +\item Any directory whose group is the primary group of the user used to perform the build must have + its group be that of the root user. +\end{compactitem} + +On SELinux systems, the SELinux context must also be preserved. Other directory attributes may be discarded. + +\subsection{Empty Directories} + +Behaviour upon encountering an empty directory is undefined. Ebuilds must not attempt to install an +empty directory. + +\section{Regular Files} + +Regular files are merged onto the filesystem (but see the notes on configuration file protection, +below). The method used to perform the merge is not specified, so long as the end result is correct. +In particular, merging a regular file may alter or remove the source file under \t{D}. + +Ebuilds must not attempt to merge a regular file on top of any existing file that is not either a +regular file or a symlink to a regular file. + +\subsection{Permissions} + +The owner, group and mode (including set*id and sticky bits) of the file must be preserved, except +as follows: + +\begin{compactitem} +\item Any file owned by the user used to perform the build must become owned by the root user. +\item Any file whose group is the primary group of the user used to perform the build must have + its group be that of the root user. +\item The package manager may reduce read and write permissions on executable files that have a + set*id bit set. +\end{compactitem} + +On SELinux systems, the SELinux context must also be preserved. Other file attributes may be discarded. + +\subsection{Configuration File Protection} +\label{config-protect} + +The package manager must provide a means to prevent user configuration files from being +overwritten by any package updates. The profile variables \t{CONFIG\_PROTECT} and +\t{CONFIG\_PROTECT\_MASK} (section~\ref{profile-variables}) control the paths for which this +must be enforced. + +In order to ensure interoperability with configuration update tools, the following scheme must be +used by all package managers when merging any regular file: + +\begin{compactenum} +\item If the directory containing the file to be merged is not listed in \t{CONFIG\_PROTECT}, and + is not a subdirectory of any such directory, and if the file is not listed in \t{CONFIG\_PROTECT}, + the file is merged normally. +\item If the directory containing the file to be merged is listed in \t{CONFIG\_PROTECT\_MASK}, or + is a subdirectory of such a directory, or if the file is listed in \t{CONFIG\_PROTECT\_MASK}, + the file is merged normally. +\item If no existing file with the intended filename exists, or the existing file has identical + content to the one being merged, the file is installed normally. +\item Otherwise, prepend the filename with \t{.\_cfg0000\_}. If no file with the new name exists, + then the file is merged with this name. +\item Otherwise, increment the number portion (to form \t{.\_cfg0001\_<name>}) and repeat step 4. + Continue this process until a usable filename is found. +\item If 9999 is reached in this way, behaviour is undefined. +\end{compactenum} + +\section{Symlinks} + +Symlinks are merged as symlinks onto the filesystem. The link destination for a merged link shall be +the same as the link destination for the link under \t{D}, except as noted below. The method used to +perform the merge is not specified, so long as the end result is correct; in particular, merging a +symlink may alter or remove the symlink under \t{D}. + +Ebuilds must not attempt to merge a symlink on top of a directory. + +\subsection{Rewriting} + +Any absolute symlink whose link starts with \t{D} must be rewritten with the leading \t{D} removed. +The package manager should issue a notice when doing this. + +\section{Hard links} + +A hard link may be merged either as a single file with links or as multiple independent files. + +\section{Other Files} + +Ebuilds must not attempt to install any other type of file (FIFOs, device nodes etc). + +% vim: set filetype=tex fileencoding=utf8 et tw=100 spell spelllang=en : + +%%% Local Variables: +%%% mode: latex +%%% TeX-master: "pms" +%%% End: |