81/118: findRoots(): Prevent a call to lstat()

[Ludovic Courtès]

civodul pushed a commit to branch nix
in repository guix.

commit 666c9b7108e460f0d3450015a3379bfeb3e3a497
Author: Eelco Dolstra <address@hidden>
Date:   Fri Aug 1 17:20:25 2014 +0200

    findRoots(): Prevent a call to lstat()
    
    This means that getting the roots from /nix/var/nix/.../hydra-roots
    doesn't need any I/O other than reading the directory.
---
 nix/libstore/gc.cc |   23 ++++++++++++++---------
 1 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/nix/libstore/gc.cc b/nix/libstore/gc.cc
index e869745..00bf152 100644
--- a/nix/libstore/gc.cc
+++ b/nix/libstore/gc.cc
@@ -294,18 +294,23 @@ static void foundRoot(StoreAPI & store,
 }
 
 
-static void findRoots(StoreAPI & store, const Path & path, Roots & roots)
+static void findRoots(StoreAPI & store, const Path & path, unsigned char type, 
Roots & roots)
 {
     try {
 
-        struct stat st = lstat(path);
+        if (type == DT_UNKNOWN) {
+            struct stat st = lstat(path);
+            if (S_ISDIR(st.st_mode)) type = DT_DIR;
+            else if (S_ISLNK(st.st_mode)) type = DT_LNK;
+            else if (S_ISREG(st.st_mode)) type = DT_REG;
+        }
 
-        if (S_ISDIR(st.st_mode)) {
+        if (type == DT_DIR) {
             for (auto & i : readDirectory(path))
-                findRoots(store, path + "/" + i.name, roots);
+                findRoots(store, path + "/" + i.name, i.type, roots);
         }
 
-        else if (S_ISLNK(st.st_mode)) {
+        else if (type == DT_LNK) {
             Path target = readLink(path);
             if (isInStore(target))
                 foundRoot(store, path, target, roots);
@@ -327,7 +332,7 @@ static void findRoots(StoreAPI & store, const Path & path, 
Roots & roots)
             }
         }
 
-        else if (S_ISREG(st.st_mode)) {
+        else if (type == DT_REG) {
             Path storePath = settings.nixStore + "/" + baseNameOf(path);
             if (store.isValidPath(storePath))
                 roots[path] = storePath;
@@ -350,9 +355,9 @@ Roots LocalStore::findRoots()
     Roots roots;
 
     /* Process direct roots in {gcroots,manifests,profiles}. */
-    nix::findRoots(*this, settings.nixStateDir + "/" + gcRootsDir, roots);
-    nix::findRoots(*this, settings.nixStateDir + "/manifests", roots);
-    nix::findRoots(*this, settings.nixStateDir + "/profiles", roots);
+    nix::findRoots(*this, settings.nixStateDir + "/" + gcRootsDir, DT_UNKNOWN, 
roots);
+    nix::findRoots(*this, settings.nixStateDir + "/manifests", DT_UNKNOWN, 
roots);
+    nix::findRoots(*this, settings.nixStateDir + "/profiles", DT_UNKNOWN, 
roots);
 
     return roots;
 }