52/64: Shortcut already-hardlinked files

[Ludovic Courtès]

civodul pushed a commit to branch nix
in repository guix.

commit a84f503d863fd77de9b6ecf149399c2ca7642b75
Author: wmertens <address@hidden>
Date:   Sat May 10 15:53:01 2014 +0200

    Shortcut already-hardlinked files
    
    If an inode in the Nix store has more than 1 link, it probably means that 
it was linked into .links/ by us. If so, skip.
    
    There's a possibility that something else hardlinked the file, so it would 
be nice to be able to override this.
    
    Also, by looking at the number of hardlinks for each of the files in 
.links/, you can get deduplication numbers and space savings.
---
 src/libstore/optimise-store.cc |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index d833f3a..1b81f64 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -71,6 +71,16 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const 
Path & path)
         return;
     }
 
+    stats.totalFiles++;
+
+    /* If a store inode has 2 or more links we presume that it was
+       already linked by us */
+    /* TODO: allow overriding this behavior */
+    if (st.st_nlink > 1) {
+        printMsg(lvlDebug, format("`%1%' is already linked, with %2% other 
file(s).") % path % (st.st_nlink - 2));
+        return;
+    }
+
     /* Hash the file.  Note that hashPath() returns the hash over the
        NAR serialisation, which includes the execute bit on the file.
        Thus, executable and non-executable files with the same
@@ -81,7 +91,6 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const 
Path & path)
        contents of the symlink (i.e. the result of readlink()), not
        the contents of the target (which may not even exist). */
     Hash hash = hashPath(htSHA256, path).first;
-    stats.totalFiles++;
     printMsg(lvlDebug, format("`%1%' has hash `%2%'") % path % 
printHash(hash));
 
     /* Check if this is a known hash. */