Re: [PATCH 01/13 V2] xfs_db: Allow writes of corrupted data by optionally skipping write verifiers

[Brian Foster <bfoster@redhat.com>]

On Mon, Mar 23, 2015 at 03:00:12PM -0500, Eric Sandeen wrote:
> Being able to write corrupt data is handy if we wish to test
> repair against specific types of corruptions.
> 
> Add a "-c" option to the write command which allows this by removing
> the write verifier.
> 
> Note that this also skips CRC updates; it's not currently possible
> to write invalid data with a valid CRC; CRC recalculation is
> intertwined with validation.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> 
> V2: Fix whitespace, remove "if (argc)", and test for
> iocur_top->bp->b_ops before attempting to deref it.
> 
> diff --git a/db/io.c b/db/io.c
> index 7f1b76a..c5898f1 100644
> --- a/db/io.c
> +++ b/db/io.c
> @@ -457,6 +457,13 @@ write_cur_bbs(void)
>  }
>  
>  void
> +xfs_dummy_verify(
> +	struct xfs_buf *bp)
> +{
> +	return;
> +}
> +
> +void
>  write_cur(void)
>  {
>  	if (iocur_sp < 0) {
> diff --git a/db/io.h b/db/io.h
> index 71082e6..31d96b4 100644
> --- a/db/io.h
> +++ b/db/io.h
> @@ -63,6 +63,7 @@ extern void	set_cur(const struct typ *t, __int64_t d, int c, int ring_add,
>  			bbmap_t *bbmap);
>  extern void     ring_add(void);
>  extern void	set_iocur_type(const struct typ *t);
> +extern void	xfs_dummy_verify(struct xfs_buf *bp);
>  
>  /*
>   * returns -1 for unchecked, 0 for bad and 1 for good
> diff --git a/db/write.c b/db/write.c
> index a0f14f4..655b618 100644
> --- a/db/write.c
> +++ b/db/write.c
> @@ -38,7 +38,7 @@ static int	write_f(int argc, char **argv);
>  static void     write_help(void);
>  
>  static const cmdinfo_t	write_cmd =
> -	{ "write", NULL, write_f, 0, -1, 0, N_("[field or value]..."),
> +	{ "write", NULL, write_f, 0, -1, 0, N_("[-c] [field or value]..."),
>  	  N_("write value to disk"), write_help };
>  
>  void
> @@ -79,6 +79,7 @@ write_help(void)
>  "  String mode: 'write \"This_is_a_filename\" - write null terminated string.\n"
>  "\n"
>  " In data mode type 'write' by itself for a list of specific commands.\n\n"
> +" Specifying the -c option will allow writes of invalid (corrupt) data.\n\n"
>  ));
>  
>  }
> @@ -90,6 +91,10 @@ write_f(
>  {
>  	pfunc_t	pf;
>  	extern char *progname;
> +	int c;
> +	int corrupt = 0;		/* Allow write of corrupt data; skip verification */
> +	struct xfs_buf_ops nowrite_ops;
> +	const struct xfs_buf_ops *stashed_ops = NULL;
>  
>  	if (x.isreadonly & LIBXFS_ISREADONLY) {
>  		dbprintf(_("%s started in read only mode, writing disabled\n"),
> @@ -109,12 +114,34 @@ write_f(
>  		return 0;
>  	}
>  
> -	/* move past the "write" command */
> -	argc--;
> -	argv++;
> +	while ((c = getopt(argc, argv, "c")) != EOF) {
> +		switch (c) {
> +		case 'c':
> +			corrupt = 1;
> +			break;
> +		default:
> +			dbprintf(_("bad option for write command\n"));
> +			return 0;
> +		}
> +	}
> +
> +	argc -= optind;
> +	argv += optind;
> +
> +	if (iocur_top->bp->b_ops && corrupt) {
> +		/* Temporarily remove write verifier to write bad data */
> +		stashed_ops = iocur_top->bp->b_ops;
> +		nowrite_ops.verify_read = stashed_ops->verify_read;
> +		nowrite_ops.verify_write = xfs_dummy_verify;
> +		iocur_top->bp->b_ops = &nowrite_ops;
> +		dbprintf(_("Allowing write of corrupted data\n"));
> +	}
>  
>  	(*pf)(DB_WRITE, cur_typ->fields, argc, argv);
>  
> +	if (stashed_ops)
> +		iocur_top->bp->b_ops = stashed_ops;
> +
>  	return 0;
>  }
>  
> diff --git a/man/man8/xfs_db.8 b/man/man8/xfs_db.8
> index 4d8d4ff..d527230 100644
> --- a/man/man8/xfs_db.8
> +++ b/man/man8/xfs_db.8
> @@ -711,7 +711,7 @@ and
>  bits respectively, and their string equivalent reported
>  (but no modifications are made).
>  .TP
> -.BI "write [" "field value" "] ..."
> +.BI "write [\-c] [" "field value" "] ..."
>  Write a value to disk.
>  Specific fields can be set in structures (struct mode),
>  or a block can be set to data values (data mode),
> @@ -729,6 +729,12 @@ contents of the block can be shifted or rotated left or right, or filled
>  with a sequence, a constant value, or a random value. In this mode
>  .B write
>  with no arguments gives more information on the allowed commands.
> +.RS 1.0i
> +.TP 0.4i
> +.B \-c
> +Skip write verifiers and CRC recalculation; allows invalid data to be written
> +to disk.
> +.RE
>  .SH TYPES
>  This section gives the fields in each structure type and their meanings.
>  Note that some types of block cover multiple actual structures,
> 
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> xfs@oss.sgi.com
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