Re: [PATCH v5 2/2] xfs_repair: new secondary superblock search method

[Eric Sandeen <sandeen@sandeen.net>]

On 2/15/16 11:00 AM, Bill O'Donnell wrote:
> xfs_repair: new secondary superblock search method
> 
> 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.
> 
> version history:
> ----
> v1: http://oss.sgi.com/archives/xfs/2016-02/msg00304.html
> v2: patch 2 whitespace fixups
> v3: patch 2 correct functionality; style fixups
> v4: patch 1,2 properly see to style and whitespace fixups
> v5: patch 2 move guess_default_geometry() to sb.c plus
>     very minor style/whitespace fixups.
> ----
> 
> Signed-off-by: Bill O'Donnell <billodo@redhat.com>

Looks good to me, thanks Bill!

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

> ---
>  Makefile        |  2 +-
>  repair/Makefile |  4 ++--
>  repair/sb.c     | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
>  3 files changed, 70 insertions(+), 8 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/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..7e4708c 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;
> @@ -117,7 +123,7 @@ 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.
>  		 */
> @@ -166,7 +172,63 @@ find_secondary_sb(xfs_sb_t *rsb)
>  	}
>  
>  	free(sb);
> -	return(retval);
> +	return retval;
> +}
> +
> +static 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;
> +}
> +
> +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.
> +	 * Failing that, fallback to a fine-grained approach.
> +	 */
> +	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: Start at min agsize and scan all blocks
> +		 */
> +		retval = __find_secondary_sb(rsb, XFS_AG_MIN_BYTES, BSIZE);
> +	}
> +	return retval;
>  }
>  
>  /*
> 

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