Stop wear-leveling during migration

Stop proactively relocate blocks during migrations, this can cause a number of
failure states such: clobbering the v1 superblock if we relocate root, and
invalidating directory pointers if we relocate the head of a directory. On top
of this, relocations increase the overall complexity of lfs_migration, which is
already a delicate operation.

Makefile

@@ -55,6 +55,7 @@ test: \
 	test_attrs \
 	test_move \
 	test_orphan \
+	test_relocations \
 	test_corrupt
 	@rm test.c
 test_%: tests/test_%.sh

lfs.c

@@ -2068,14 +2068,10 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
     dir->pos = lfs_min(2, off);
     off -= dir->pos;
 
-    // skip superblock entry
-    dir->id = (off > 0 && lfs_pair_cmp(dir->head, lfs->root) == 0);
-
-    while (off > 0) {
-        int diff = lfs_min(dir->m.count - dir->id, off);
-        dir->id += diff;
-        dir->pos += diff;
-        off -= diff;
+    while (off != 0) {
+        dir->id = lfs_min(dir->m.count, off);
+        dir->pos += dir->id;
+        off -= dir->id;
 
         if (dir->id == dir->m.count) {
             if (!dir->m.split) {
@@ -2088,8 +2084,6 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
                 LFS_TRACE("lfs_dir_seek -> %d", err);
                 return err;
             }
-
-            dir->id = 0;
         }
     }
 
@@ -2113,8 +2107,6 @@ int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir) {
         return err;
     }
 
-    dir->m.pair[0] = dir->head[0];
-    dir->m.pair[1] = dir->head[1];
     dir->id = 0;
     dir->pos = 0;
     LFS_TRACE("lfs_dir_rewind -> %d", 0);
@@ -3897,6 +3889,12 @@ static int lfs_fs_relocate(lfs_t *lfs,
             d->m.pair[0] = newpair[0];
             d->m.pair[1] = newpair[1];
         }
+
+        if (d->type == LFS_TYPE_DIR &&
+                lfs_pair_cmp(oldpair, ((lfs_dir_t*)d)->head) == 0) {
+            ((lfs_dir_t*)d)->head[0] = newpair[0];
+            ((lfs_dir_t*)d)->head[1] = newpair[1];
+        }
     }
 
     // find parent

tests/test_relocations.sh

@@ -0,0 +1,88 @@
+#!/bin/bash
+set -eu
+export TEST_FILE=$0
+trap 'export TEST_LINE=$LINENO' DEBUG
+
+ITERATIONS=20
+COUNT=10
+
+echo "=== Relocation tests ==="
+rm -rf blocks
+scripts/test.py << TEST
+    lfs_format(&lfs, &cfg) => 0;
+    // fill up filesystem so only ~16 blocks are left
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, "padding", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    memset(buffer, 0, 512);
+    while (LFS_BLOCK_COUNT - lfs_fs_size(&lfs) > 16) {
+        lfs_file_write(&lfs, &file, buffer, 512) => 512;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    // make a child dir to use in bounded space
+    lfs_mkdir(&lfs, "child") => 0;
+    lfs_unmount(&lfs) => 0;
+TEST
+
+echo "--- Outdated head test ---"
+scripts/test.py << TEST
+    lfs_mount(&lfs, &cfg) => 0;
+    for (int j = 0; j < $ITERATIONS; j++) {
+        for (int i = 0; i < $COUNT; i++) {
+            sprintf(path, "child/test%03d_loooooooooooooooooong_name", i);
+            lfs_file_open(&lfs, &file, path, LFS_O_CREAT | LFS_O_WRONLY) => 0;
+            lfs_file_close(&lfs, &file) => 0;
+        }
+
+        lfs_dir_open(&lfs, &dir, "child") => 0;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        for (int i = 0; i < $COUNT; i++) {
+            sprintf(path, "test%03d_loooooooooooooooooong_name", i);
+            lfs_dir_read(&lfs, &dir, &info) => 1;
+            strcmp(info.name, path) => 0;
+            info.size => 0;
+
+            sprintf(path, "child/test%03d_loooooooooooooooooong_name", i);
+            lfs_file_open(&lfs, &file, path, LFS_O_WRONLY) => 0;
+            lfs_file_write(&lfs, &file, "hi", 2) => 2;
+            lfs_file_close(&lfs, &file) => 0;
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 0;
+
+        lfs_dir_rewind(&lfs, &dir) => 0;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        for (int i = 0; i < $COUNT; i++) {
+            sprintf(path, "test%03d_loooooooooooooooooong_name", i);
+            lfs_dir_read(&lfs, &dir, &info) => 1;
+            strcmp(info.name, path) => 0;
+            info.size => 2;
+
+            sprintf(path, "child/test%03d_loooooooooooooooooong_name", i);
+            lfs_file_open(&lfs, &file, path, LFS_O_WRONLY) => 0;
+            lfs_file_write(&lfs, &file, "hi", 2) => 2;
+            lfs_file_close(&lfs, &file) => 0;
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 0;
+
+        lfs_dir_rewind(&lfs, &dir) => 0;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        for (int i = 0; i < $COUNT; i++) {
+            sprintf(path, "test%03d_loooooooooooooooooong_name", i);
+            lfs_dir_read(&lfs, &dir, &info) => 1;
+            strcmp(info.name, path) => 0;
+            info.size => 2;
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 0;
+        lfs_dir_close(&lfs, &dir) => 0;
+
+        for (int i = 0; i < $COUNT; i++) {
+            sprintf(path, "child/test%03d_loooooooooooooooooong_name", i);
+            lfs_remove(&lfs, path) => 0;
+        }
+    }
+    lfs_unmount(&lfs) => 0;
+TEST
+
+scripts/results.py

tests/test_seek.sh

@@ -428,78 +428,4 @@ scripts/test.py << TEST
 TEST
 done
 
-echo "--- Root seek test ---"
-./scripts/test.py << TEST
-    lfs_mount(&lfs, &cfg) => 0;
-    for (int i = 3; i < $MEDIUMSIZE; i++) {
-        sprintf(path, "hi%03d", i);
-        lfs_mkdir(&lfs, path) => 0;
-    }
-
-    lfs_dir_open(&lfs, &dir, "/") => 0;
-    for (int i = 0; i < $MEDIUMSIZE; i++) {
-        if (i == 0) {
-            sprintf(path, ".");
-        } else if (i == 1) {
-            sprintf(path, "..");
-        } else if (i == 2) {
-            sprintf(path, "hello");
-        } else {
-            sprintf(path, "hi%03d", i);
-        }
-        lfs_dir_read(&lfs, &dir, &info) => 1;
-        strcmp(path, info.name) => 0;
-    }
-    lfs_dir_read(&lfs, &dir, &info) => 0;
-    lfs_dir_close(&lfs, &dir) => 0;
-
-    for (int j = 0; j < $MEDIUMSIZE; j++) {
-        lfs_soff_t off = -1;
-
-        lfs_dir_open(&lfs, &dir, "/") => 0;
-        for (int i = 0; i < $MEDIUMSIZE; i++) {
-            if (i == 0) {
-                sprintf(path, ".");
-            } else if (i == 1) {
-                sprintf(path, "..");
-            } else if (i == 2) {
-                sprintf(path, "hello");
-            } else {
-                sprintf(path, "hi%03d", i);
-            }
-
-            if (i == j) {
-                off = lfs_dir_tell(&lfs, &dir);
-                off >= 0 => true;
-            }
-
-            lfs_dir_read(&lfs, &dir, &info) => 1;
-            strcmp(path, info.name) => 0;
-        }
-        lfs_dir_read(&lfs, &dir, &info) => 0;
-        lfs_dir_close(&lfs, &dir) => 0;
-
-        lfs_dir_open(&lfs, &dir, "/") => 0;
-        lfs_dir_seek(&lfs, &dir, off) => 0;
-        for (int i = j; i < $MEDIUMSIZE; i++) {
-            if (i == 0) {
-                sprintf(path, ".");
-            } else if (i == 1) {
-                sprintf(path, "..");
-            } else if (i == 2) {
-                sprintf(path, "hello");
-            } else {
-                sprintf(path, "hi%03d", i);
-            }
-
-            lfs_dir_read(&lfs, &dir, &info) => 1;
-            strcmp(path, info.name) => 0;
-        }
-        lfs_dir_read(&lfs, &dir, &info) => 0;
-        lfs_dir_close(&lfs, &dir) => 0;
-    }
-
-    lfs_unmount(&lfs) => 0;
-TEST
-
 scripts/results.py