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* Simplify communication with the hook a bit (don't use file

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descriptors 3/4, just use stdin/stderr).
This commit is contained in:
Eelco Dolstra 2009-03-28 19:29:55 +00:00
parent 7fb548aa26
commit 3a2bbe7f8a
6 changed files with 68 additions and 117 deletions
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51
doc/manual/env-common.xml
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@ -151,12 +151,12 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
<para>On the basis of this information, and whatever persistent
state the build hook keeps about other machines and their current
load, it has to decide what to do with the build. It should print
out on file descriptor 3 one of the following responses (terminated
by a newline, <literal>"\n"</literal>):
out on standard error one of the following responses (terminated by
a newline, <literal>"\n"</literal>):
<variablelist>
<varlistentry><term><literal>decline</literal></term>
<varlistentry><term><literal># decline</literal></term>
<listitem><para>The build hook is not willing or able to perform
the build; the calling Nix process should do the build itself,
@ -164,7 +164,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
</varlistentry>
<varlistentry><term><literal>postpone</literal></term>
<varlistentry><term><literal># postpone</literal></term>
<listitem><para>The build hook cannot perform the build now, but
can do so in the future (e.g., because all available build slots
@ -174,7 +174,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
</varlistentry>
<varlistentry><term><literal>accept</literal></term>
<varlistentry><term><literal># accept</literal></term>
<listitem><para>The build hook has accepted the
build.</para></listitem>
@ -185,37 +185,12 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
</para>
<para>If the build hook accepts the build, it is possible that it is
no longer necessary to do the build because some other process has
performed the build in the meantime. To prevent races, the hook
must read from file descriptor 4 a single line that tells it whether
to continue:
<variablelist>
<varlistentry><term><literal>cancel</literal></term>
<listitem><para>The build has already been done, so the hook
should exit.</para></listitem>
</varlistentry>
<varlistentry><term><literal>okay</literal></term>
<listitem><para>The hook should proceed with the build. At this
point, the calling Nix process has acquired locks on the output
path, so no other Nix process will perform the
build.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>If the hook has been told to proceed, Nix will store in the
hook’s current directory a number of text files that contain
information about the derivation:
<para>After sending <literal># accept</literal>, the hook should
read one line from standard input, which will be the string
<literal>okay</literal>. It can then proceed with the build.
Before sending <literal>okay</literal>, Nix will store in the hook’s
current directory a number of text files that contain information
about the derivation:
<variablelist>
@ -255,7 +230,9 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
<para>The hook should copy the inputs to the remote machine,
register the validity of the inputs, perform the remote build, and
copy the outputs back to the local machine. An exit code other than
<literal>0</literal> indicates that the hook has failed.</para>
<literal>0</literal> indicates that the hook has failed. An exit
code equal to 100 means that the remote build failed (as opposed to,
e.g., a network error).</para>
</listitem>