[PATCH v4 2/2] xfs_repair: new secondary superblock search method

["Bill O'Donnell" <billodo@xxxxxxxxxx>]

Optimize secondary sb search, using similar method to find
fs geometry as that of xfs_mkfs. If this faster method fails
in finding a secondary sb, fall back to original brute force
slower search.

Signed-off-by: Bill O'Donnell <billodo@xxxxxxxxxx>
---
 Makefile           |  2 +-
 include/libxcmd.h  |  6 +++++-
 libxcmd/topology.c | 27 +++++++++++++++++++++++++++
 repair/Makefile    |  4 ++--
 repair/sb.c        | 49 +++++++++++++++++++++++++++++++++++++++++--------
 5 files changed, 76 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index fca0a42..1d60d9c 100644
--- a/Makefile
+++ b/Makefile
@@ -80,7 +80,7 @@ fsr: libhandle
 growfs: libxcmd
 io: libxcmd libhandle
 quota: libxcmd
-repair: libxlog
+repair: libxlog libxcmd
 copy: libxlog
 
 ifeq ($(HAVE_BUILDDEFS), yes)
diff --git a/include/libxcmd.h b/include/libxcmd.h
index a912534..eb16cd5 100644
--- a/include/libxcmd.h
+++ b/include/libxcmd.h
@@ -51,6 +51,10 @@ extern int
 check_overwrite(
        char            *device);
 
-
+extern int
+guess_default_geometry(
+       __uint64_t      *agsize,
+       __uint64_t      *agcount,
+       libxfs_init_t   x);
 
 #endif /* __LIBXCMD_H__ */
diff --git a/libxcmd/topology.c b/libxcmd/topology.c
index 4cbe4b1..ec9695c 100644
--- a/libxcmd/topology.c
+++ b/libxcmd/topology.c
@@ -339,3 +339,30 @@ get_topology(
                                   &lsectorsize, &psectorsize, force_overwrite);
        }
 }
+
+int
+guess_default_geometry(
+       __uint64_t      *agsize,
+       __uint64_t      *agcount,
+       libxfs_init_t   x)
+{
+       struct fs_topology      ft;
+       int                     blocklog;
+       __uint64_t              dblocks;
+       int                     multidisk;
+
+       memset(&ft, 0, sizeof(ft));
+       get_topology(&x, &ft, 1);
+
+       /*
+        * get geometry from get_topology result.
+        * Use default block size (2^12)
+        */
+       blocklog = 12;
+       multidisk = ft.dswidth | ft.dsunit;
+       dblocks = x.dsize >> (blocklog - BBSHIFT);
+       calc_default_ag_geometry(blocklog, dblocks, multidisk,
+                                agsize, agcount);
+
+       return blocklog;
+}
diff --git a/repair/Makefile b/repair/Makefile
index 251722b..d24ab1f 100644
--- a/repair/Makefile
+++ b/repair/Makefile
@@ -20,8 +20,8 @@ CFILES = agheader.c attr_repair.c avl.c avl64.c bmap.c 
btree.c \
        progress.c prefetch.c rt.c sb.c scan.c threads.c \
        versions.c xfs_repair.c
 
-LLDLIBS = $(LIBXFS) $(LIBXLOG) $(LIBUUID) $(LIBRT) $(LIBPTHREAD)
-LTDEPENDENCIES = $(LIBXFS) $(LIBXLOG)
+LLDLIBS = $(LIBBLKID) $(LIBXFS) $(LIBXLOG) $(LIBUUID) $(LIBRT) $(LIBPTHREAD) 
$(LIBXCMD)
+LTDEPENDENCIES = $(LIBXFS) $(LIBXLOG) $(LIBXCMD)
 LLDFLAGS = -static-libtool-libs
 
 default: depend $(LTCOMMAND)
diff --git a/repair/sb.c b/repair/sb.c
index 4eef14a..8dcad5f 100644
--- a/repair/sb.c
+++ b/repair/sb.c
@@ -17,6 +17,7 @@
  */
 
 #include "libxfs.h"
+#include "libxcmd.h"
 #include "libxlog.h"
 #include "agheader.h"
 #include "globals.h"
@@ -85,10 +86,15 @@ copy_sb(xfs_sb_t *source, xfs_sb_t *dest)
 }
 
 /*
- * find a secondary superblock, copy it into the sb buffer
+ * find a secondary superblock, copy it into the sb buffer.
+ * start is the point to begin reading BSIZE bytes.
+ * skip contains a byte-count of how far to advance for next read.
  */
-int
-find_secondary_sb(xfs_sb_t *rsb)
+static int
+__find_secondary_sb(
+       xfs_sb_t *rsb,
+       __uint64_t start,
+       __uint64_t skip)
 {
        xfs_off_t       off;
        xfs_sb_t        *sb;
@@ -101,7 +107,6 @@ find_secondary_sb(xfs_sb_t *rsb)
        int             bsize;
 
        do_warn(_("\nattempting to find secondary superblock...\n"));
-
        sb = (xfs_sb_t *)memalign(libxfs_device_alignment(), BSIZE);
        if (!sb) {
                do_error(
@@ -117,7 +122,7 @@ find_secondary_sb(xfs_sb_t *rsb)
        /*
         * skip first sector since we know that's bad
         */
-       for (done = 0, off = XFS_AG_MIN_BYTES; !done ; off += bsize)  {
+       for (done = 0, off = start; !done ; off += skip)  {
                /*
                 * read disk 1 MByte at a time.
                 */
@@ -128,9 +133,7 @@ find_secondary_sb(xfs_sb_t *rsb)
                if (!done && (bsize = read(x.dfd, sb, BSIZE)) <= 0)  {
                        done = 1;
                }
-
                do_warn(".");
-
                /*
                 * check the buffer 512 bytes at a time since
                 * we don't know how big the sectors really are.
@@ -166,7 +169,37 @@ find_secondary_sb(xfs_sb_t *rsb)
        }
 
        free(sb);
-       return(retval);
+       return retval;
+}
+
+int
+find_secondary_sb(xfs_sb_t *rsb)
+{
+       int             retval;
+       __uint64_t      agcount;
+       __uint64_t      agsize;
+       __uint64_t      skip;
+       int             blocklog;
+
+       /*
+        * Attempt to find secondary sb with a coarse approach,
+        * using a large skip (agsize in bytes). Failing that,
+        * fallback to the fine-grained approach using min agsize.
+        */
+       blocklog = guess_default_geometry(&agsize, &agcount, x);
+
+       /*
+        * use found ag geometry to quickly find secondary sb
+        */
+       skip = agsize << blocklog;
+       retval = __find_secondary_sb(rsb, skip, skip);
+       if (!retval)  {
+               /*
+                * fallback: use minimum agsize for skipsize
+                */
+               retval = __find_secondary_sb(rsb, XFS_AG_MIN_BYTES, BSIZE);
+       }
+       return retval;
 }
 
 /*
-- 
2.5.0