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* nix-pull now requires the full url to the manifest, i.e., `/MANIFEST/' is no longer automatically appended. * nix-prefetch-url works again.
115 lines
4.5 KiB
XML
115 lines
4.5 KiB
XML
<appendix>
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<title>Bugs / To-Do</title>
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<itemizedlist>
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<listitem>
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<para>
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The man-pages generated from the DocBook documentation are ugly.
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</para>
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</listitem>
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<listitem>
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<para>
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Generations properly form a tree. E.g., if after switching to
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generation 39, we perform an installation action, a generation
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43 is created which is a descendant of 39, not 42. So a
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rollback from 43 ought to go back to 39. This is not
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currently implemented; generations form a linear sequence.
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</para>
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</listitem>
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<listitem>
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<para>
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Unify the concepts of successors and substitutes into a
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general notion of <emphasis>equivalent expressions</emphasis>.
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Expressions are equivalent if they have the same target paths
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with the same identifiers. However, even though they are
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functionally equivalent, they may differ stronly with respect
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to their <emphasis>performance characteristics</emphasis>.
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For example, realising a closure expression is more efficient
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that realising the derivation expression from which it was
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produced. On the other hand, distributing sources may be more
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efficient (storage- or bandwidth-wise) than distributing
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binaries. So we need to be able to attach weigths or
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priorities or performance annotations to expressions; Nix can
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then choose the most efficient expression dependent on the
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context.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>Build management.</emphasis> In principle it is already
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possible to do build management using Nix (by writing builders that
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perform appropriate build steps), but the Nix expression language is
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not yet powerful enough to make this pleasant (?). The language should
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be extended with features from the <ulink
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url='http://www.cs.uu.nl/~eelco/maak/'>Maak build manager</ulink>.
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Another interesting idea is to write a <command>make</command>
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implementation that uses Nix as a back-end to support <ulink
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url='http://www.research.att.com/~bs/bs_faq.html#legacy'>legacy</ulink>
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build files.
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</para>
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</listitem>
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<listitem>
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<para>
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The current garbage collector is a hack. It should be
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integrated into <command>nix-store</command>. It should
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delete derivations in an order determined by topologically
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sorting derivations under the points-to relation. This
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ensures that no store paths ever exist that point to
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non-existant store paths.
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</para>
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</listitem>
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<listitem>
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<para>
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There are race conditions between the garbage collector and
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other Nix tools. For instance, when we run
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<command>nix-env</command> to build and install a derivation
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and run the garbage collector at the same time, the garbage
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collector may kick in exactly between the build and
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installation steps, i.e., before the newly built derivation
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has become reachable from a root of the garbage collector.
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</para>
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<para>
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One solution would be for these programs to properly register
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temporary roots for the collector. Another would be to use
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stop-the-world garbage collection: if any tool is running, the
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garbage collector blocks, and vice versa. These solutions do
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not solve the situation where multiple tools are involved,
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e.g.,
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<screen>
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$ nix-store -r $(nix-instantiate foo.nix)</screen>
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since even if <command>nix-instantiate</command> where to
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register a temporary root, it would be released by the time
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<command>nix-store</command> is started. A solution would be
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to write the intermediate value to a file that is used as a
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root to the collector, e.g.,
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<screen>
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$ nix-instantiate foo.nix > /nix/var/nix/roots/bla
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$ nix-store -r $(cat /nix/var/nix/roots/bla)</screen>
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</para>
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</listitem>
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<listitem>
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<para>
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For security, <command>nix-push</command> manifests should be
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digitally signed, and <command>nix-pull</command> should
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verify the signatures. The actual NAR archives in the cache
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do not need to be signed, since the manifest contains
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cryptographic hashes of these files (and
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<filename>fetchurl.nix</filename> checks them).
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</para>
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</listitem>
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</itemizedlist>
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</appendix>
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