This mounts an arbitrary Nix store on the specified mount point.
Typical usage:
$ /nix/store/d0am5d8gwh2kfdcgyxh4y684mb5b2v54-blender-2.79/bin/blender --version
bash: /nix/store/d0am5d8gwh2kfdcgyxh4y684mb5b2v54-blender-2.79/bin/blender: No such file or directory
$ nix mount-store /tmp/mp --store https://cache.nixos.org?local-nar-cache=/tmp/nars
$ unshare -m -r
$ mount -o bind /tmp/mp /nix/store
$ /nix/store/d0am5d8gwh2kfdcgyxh4y684mb5b2v54-blender-2.79/bin/blender --version
[after a lot of downloading...]
Blender 2.79 (sub 0)
One application is to replace the current remote store file access in
hydra-server implemented via "nix {cat,ls}-store", which doesn't work
all that well (e.g. it doesn't resolve symlinks properly).
Another application would be on-demand fetching of build inputs on
Hydra build slaves (to speed up builds that don't access their entire
closure). However, that will require a lot more machinery.
E.g.
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
/nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
real 0m4.139s
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
/nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
real 0m0.024s
(Before, the second call took ~0.220s.)
This will use a NAR listing in
/tmp/nars/b0w2hafndl09h64fhb86kw6bmhbmnpm1.ls containing all metadata,
including the offsets of regular files inside the NAR. Thus, we don't
need to read the entire NAR. (We do read the entire listing, but
that's generally pretty small. We could use a SQLite DB by borrowing
some more code from nixos-channel-scripts/file-cache.hh.)
This is primarily useful when Hydra is serving files from an S3 binary
cache, in particular when you have giant NARs. E.g. we had some 12 GiB
NARs, so accessing individuals files was pretty slow.
propagated-user-env-packages files in nixpkgs aren't all terminated by
newlines, as buildenv expected. Now it does not require a terminating
newline; note that this introduces a behaviour change: propagated user
env packages may now be spread across multiple lines. However, nix
1.11.x still expects them to be on a single line so this shouldn't be
used in nixpkgs for now.
The storeUri variable in the build-remote hook is declared very much to
the start of the main function and a bunch of lines later, the same
variable gets checked via hasPrefix() but it gets assigned *after* that
check when the most suitable machine for the build was choosen.
So I guess this was just a typo in d16fd24973
and what we really want is to either checkd the prefix *after* assigning
storeUri or use bestMachine->storeUri directly.
I choose the latter, because the former could introduce even more
regressions if the try block where the variable gets assigned terminates
early.
Nevertheless, the reason why the log output didn't work is because
hasPrefix() checked for "ssh://" in front of storeUri, but if the
storeUri isn't set correctly (or at all), we don't get the log file
descriptor set up properly, leading to no log output.
I've adjusted the remote-builds test to include a regression test for
this, so that we can make sure we get a build output when using remote
builds.
In addition to that I've tested this with two of my build farms and the
build logs are emitted correctly again.
Signed-off-by: aszlig <aszlig@nix.build>
