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It turns out that in multi-user Nix, a builder may be able to do
ln /etc/shadow $out/foo
Afterwards, canonicalisePathMetaData() will be applied to $out/foo,
causing /etc/shadow's mode to be set to 444 (readable by everybody but
writable by nobody). That's obviously Very Bad.
Fortunately, this fails in NixOS's default configuration because
/nix/store is a bind mount, so "ln" will fail with "Invalid
cross-device link". It also fails if hard-link restrictions are
enabled, so a workaround is:
echo 1 > /proc/sys/fs/protected_hardlinks
The solution is to check that all files in $out are owned by the build
user. This means that innocuous operations like "ln
${pkgs.foo}/some-file $out/" are now rejected, but that already failed
in chroot builds anyway.
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...where <XX> is the first two characters of the derivation.
Otherwise /nix/var/log/nix/drvs may become so large that we run into
all sorts of weird filesystem limits/inefficiences. For instance,
ext3/ext4 filesystems will barf with "ext4_dx_add_entry:1551:
Directory index full!" once you hit a few million files.
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Doing this once makes subsequent operations like garbage collecting
more efficient since we don't have to call makeMutable() first.
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substituter
Issue #77.
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Fixes #77.
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Fixes #24.
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Waiting for the hook to shut down cleanly sometimes seems to lead to
hangs.
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This reverts commit cc511fd65b7b6de9e87e72fb4bed16fc7efeb8b7.
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If a derivation has multiple outputs, then we only want to download
those outputs that are actuallty needed. So if we do "nix-build -A
openssl.man", then only the "man" output should be downloaded.
Likewise if another package depends on ${openssl.man}.
The tricky part is that different derivations can depend on different
outputs of a given derivation, so we may need to restart the
corresponding derivation goal if that happens.
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For example, given a derivation with outputs "out", "man" and "bin":
$ nix-build -A pkg
produces ./result pointing to the "out" output;
$ nix-build -A pkg.man
produces ./result-man pointing to the "man" output;
$ nix-build -A pkg.all
produces ./result, ./result-man and ./result-bin;
$ nix-build -A pkg.all -A pkg2
produces ./result, ./result-man, ./result-bin and ./result-2.
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vfork() is just too weird. For instance, in this build:
http://hydra.nixos.org/build/3330487
the value fromHook.writeSide becomes corrupted in the parent, even
though the child only reads from it. At -O0 the problem goes away.
Probably the child is overriding some spilled temporary variable.
If I get bored I may implement using posix_spawn() instead.
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Slightly scared of using std::cerr in a vforked process...
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Hopefully this reduces the chance of hitting ‘unable to fork: Cannot
allocate memory’ errors. vfork() is used for everything except
starting builders.
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They are unnecessary because we set the close-on-exec flag.
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Fixes #57.
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If we find a corrupted path in the output closure, we rebuild the
derivation that produced that particular path.
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With this flag, if any valid derivation output is missing or corrupt,
it will be recreated by using a substitute if available, or by
rebuilding the derivation. The latter may use hash rewriting if
chroots are not available.
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This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.
Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available. So
repairing should be used with some care on critical packages like
Glibc.
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Using the immutable bit is problematic, especially in conjunction with
store optimisation. For instance, if the garbage collector deletes a
file, it has to clear its immutable bit, but if the file has
additional hard links, we can't set the bit afterwards because we
don't know the remaining paths.
So now that we support having the entire Nix store as a read-only
mount, we may as well drop the immutable bit. Unfortunately, we have
to keep the code to clear the immutable bit for backwards
compatibility.
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Fixes issue #123 in Nixpkgs.
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Note that this will only work if the client has a very recent Nix
version (post 15e1b2c223494ecb5efefc3ea0e3b926a6b1d7dc), otherwise the
--option flag will just be ignored.
Fixes #50.
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Probably it's not a good idea to pass a temporary object to
StringSource.
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case)
This uses scary hash rewriting.
Fixes #21.
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This handles the chroot and build hook cases, which are easy.
Supporting the non-chroot-build case will require more work (hash
rewriting!).
Issue #21.
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http://hydra.nixos.org/build/2955671
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This is required on systemd, which mounts filesystems as "shared"
subtrees. Changes to shared trees in a private mount namespace are
propagated to the outside world, which is bad.
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Put all Nix configuration flags in a Settings object.
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Previously substituters could read nix.conf themselves, but this
didn't take --option flags into account.
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Since SubstitutionGoal::finished() in build.cc computes the hash
anyway, we can prevent the inefficiency of computing the hash twice by
letting the substituter tell Nix about the expected hash, which can
then verify it.
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Fixes #39.
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