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LocalStore: Allow the physical and logical store directories to differ

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This is primarily to subsume the functionality of the
copy-from-other-stores substituter. For example, in the NixOS
installer, we can now do (assuming we're in the target chroot, and the
Nix store of the installation CD is bind-mounted on /tmp/nix):

  $ nix-build ... --option substituters 'local?state=/tmp/nix/var&real=/tmp/nix/store'

However, unlike copy-from-other-stores, this also allows write access
to such a store. One application might be fetching substitutes for
/nix/store in a situation where the user doesn't have sufficient
privileges to create /nix, e.g.:

  $ NIX_REMOTE="local?state=/home/alice/nix/var&real=/home/alice/nix/store" nix-build ...
This commit is contained in:
Eelco Dolstra 2016-06-02 15:08:18 +02:00
parent 064816ab98
commit 4494000e04
7 changed files with 68 additions and 158 deletions
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6
src/libstore/optimise-store.cc
View file

@ -176,7 +176,7 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHa
/* Make the containing directory writable, but only if it's not
the store itself (we don't want or need to mess with its
permissions). */
bool mustToggle = !isStorePath(path);
bool mustToggle = dirOf(path) != realStoreDir;
if (mustToggle) makeWritable(dirOf(path));
/* When we're done, make the directory read-only again and reset
@ -184,7 +184,7 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHa
MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
% storeDir % getpid() % rand()).str();
% realStoreDir % getpid() % rand()).str();
if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
if (errno == EMLINK) {
@ -229,7 +229,7 @@ void LocalStore::optimiseStore(OptimiseStats & stats)
addTempRoot(i);
if (!isValidPath(i)) continue; /* path was GC'ed, probably */
Activity act(*logger, lvlChatty, format("hashing files in ‘%1%’") % i);
optimisePath_(stats, i, inodeHash);
optimisePath_(stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
}
}