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Re: [PATCH] xfs: reset buffer pointers before freeing them

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: reset buffer pointers before freeing them
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 12 Apr 2011 12:22:37 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20110412134543.GG31057@dastard>
References: <1302491405-2290-1-git-send-email-david@xxxxxxxxxxxxx> <20110412000939.GC29358@xxxxxxxxxxxxx> <20110412110028.GA31057@dastard> <20110412134543.GG31057@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Apr 12, 2011 at 11:45:43PM +1000, Dave Chinner wrote:
> Something like this?

Kinda.  A few comments below.

>  /*
> + * Read at an offset into the buffer. Returns with the buffer in it's 
> original
> + * state regardless of the result of the read.
> + */
> +STATIC int
> +xlog_bread_offset(
> +     xlog_t          *log,
> +     int             buf_offset,     /* offset into buffer */
> +     int             buf_blks,       /* original buffer size */
> +     xfs_daddr_t     blk_no,         /* block to read from */
> +     int             nbblks,         /* blocks to read */
> +     xfs_buf_t       *bp,
> +     xfs_caddr_t     offset)
> +{
> +     xfs_caddr_t     orig_offset = XFS_BUF_PTR(bp);
> +     int             error, error2;
> +
> +     error = XFS_BUF_SET_PTR(bp, offset + BBTOB(buf_offset), BBTOB(nbblks));

Passing in both offset and the buf_offset seems odd as they are only
used together.  So just passing in one byte offset would make more
sense to me.  Of course it's not actually an offset anyore, but virtual
address, but we use that offset naming all around xlog_align/xlog_bread
and callers.

Also I don't think there is a need for the buf_blks argument.  The
argument always comes directly from the xlog_get_bp number blocks
argument, so the

        BBTOB(buf_blks)

can be replaced by simply using a copy of b_buffer_length taken at
the beginning of the function.

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