06/07: daemon: optimizePath: Detect some .links corruptions.

[Ludovic Courtès]

civodul pushed a commit to branch master
in repository guix.

commit e134baae774eaa78e7ae8c3d87db50170f023536
Author: Eelco Dolstra <address@hidden>
Date:   Mon Nov 9 20:48:09 2015 +0100

    daemon: optimizePath: Detect some .links corruptions.
    
    If automatic store optimisation is enabled, and a hard-linked file in
    the store gets corrupted, then the corresponding .links entry will
    also be corrupted. In that case, trying to repair with --repair or
    --repair-path won't work, because the new "good" file will be replaced
    by a hard link to the corrupted file. We can catch most of these cases
    by doing a sanity-check on the file sizes.
---
 nix/libstore/optimise-store.cc |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/nix/libstore/optimise-store.cc b/nix/libstore/optimise-store.cc
index c62b8e4..d7508b0 100644
--- a/nix/libstore/optimise-store.cc
+++ b/nix/libstore/optimise-store.cc
@@ -120,7 +120,7 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const 
Path & path, InodeHa
         return;
     }
 
-    /* This can still happen on top-level files */
+    /* This can still happen on top-level files. */
     if (st.st_nlink > 1 && inodeHash.count(st.st_ino)) {
         printMsg(lvlDebug, format("`%1%' is already linked, with %2% other 
file(s).") % path % (st.st_nlink - 2));
         return;
@@ -141,6 +141,7 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const 
Path & path, InodeHa
     /* Check if this is a known hash. */
     Path linkPath = linksDir + "/" + printHash32(hash);
 
+ retry:
     if (!pathExists(linkPath)) {
         /* Nope, create a hard link in the links directory. */
         if (link(path.c_str(), linkPath.c_str()) == 0) {
@@ -164,7 +165,13 @@ void LocalStore::optimisePath_(OptimiseStats & stats, 
const Path & path, InodeHa
         return;
     }
 
-    printMsg(lvlTalkative, format("linking `%1%' to `%2%'") % path % linkPath);
+    if (st.st_size != stLink.st_size) {
+        printMsg(lvlError, format("removing corrupted link ‘%1%’") % linkPath);
+        unlink(linkPath.c_str());
+        goto retry;
+    }
+
+    printMsg(lvlTalkative, format("linking ‘%1%’ to ‘%2%’") % path % linkPath);
 
     /* Make the containing directory writable, but only if it's not
        the store itself (we don't want or need to mess with its