[Devel] Re: [PATCH 1/2] mm: move common segment checks to separate helper function (v6)

[Nick Piggin]

On Mon, Mar 12, 2007 at 10:57:53AM +0300, Dmitriy Monakhov wrote:
> I realy don't want to be annoying by sending this patcheset over and over
> again. If anyone think this patch is realy cappy, please comment what 
> exectly is bad. Thank you.

Doesn't seem like a bad idea.

> 
> Changes:
>   - patch was split in two patches.
>   - comments added. I think now it is clearly describe things.
>   - make generic_segment_checks() inline
>   - patch prepared against 2.6.20-mm3
> 
> How is tested:
>  - LTP test, and other readv/writev op tests.
> 
> Signed-off-by: Monakhov Dmitriy <dmonakhov at openvz.org>
> ---
>  mm/filemap.c |   76 +++++++++++++++++++++++++++++----------------------------
>  1 files changed, 39 insertions(+), 37 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 8e1849a..0aadf5f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1159,6 +1159,39 @@ success:
>  	return size;
>  }
>  
> +/*
> + * Performs necessary checks before doing a write
> + *
> + * Adjust number of segments and amount of bytes to write.
> + * Returns appropriate error code that caller should return or
> + * zero in case that write should be allowed.
> + */
> +inline int generic_segment_checks(const struct iovec *iov,
> +			unsigned long *nr_segs, size_t *count,
> +			unsigned long access_flags)

Make it static and not inline, and the compiler will work it out.

This function name doesn't really imply that it returns you the
nr_segs and count, but that's not a big deal I guess.

You also don't say that nr_segs should be initialised to the amount
you which to write, while count must be initialised to zero.

> +{
> +	unsigned long   seg;
> +	for (seg = 0; seg < *nr_segs; seg++) {
> +		const struct iovec *iv = &iov[seg];
> +
> +		/*
> +		 * If any segment has a negative length, or the cumulative
> +		 * length ever wraps negative then return -EINVAL.
> +		 */
> +		*count += iv->iov_len;
> +		if (unlikely((ssize_t)(*count|iv->iov_len) < 0))
> +			return -EINVAL;
> +		if (access_ok(access_flags, iv->iov_base, iv->iov_len))
> +			continue;

Why now insert the above test, and put the below statements inside the
branch? OTOH, that makes it less obviously c&p from the others. Maybe
a subsequent patch.

> +		if (seg == 0)
> +			return -EFAULT;
> +		*nr_segs = seg;
> +		*count -= iv->iov_len;	/* This segment is no good */
> +		break;
> +	}


You could assign to *count here, once, and remove the requirement
that the caller initialised it to zero?

> +	return 0;
> +}
> +
>  /**
>   * generic_file_aio_read - generic filesystem read routine
>   * @iocb:	kernel I/O control block
> @@ -1180,24 +1213,9 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>  	loff_t *ppos = &iocb->ki_pos;
>  
>  	count = 0;
> -	for (seg = 0; seg < nr_segs; seg++) {
> -		const struct iovec *iv = &iov[seg];
> -
> -		/*
> -		 * If any segment has a negative length, or the cumulative
> -		 * length ever wraps negative then return -EINVAL.
> -		 */
> -		count += iv->iov_len;
> -		if (unlikely((ssize_t)(count|iv->iov_len) < 0))
> -			return -EINVAL;
> -		if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
> -			continue;
> -		if (seg == 0)
> -			return -EFAULT;
> -		nr_segs = seg;
> -		count -= iv->iov_len;	/* This segment is no good */
> -		break;
> -	}
> +	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
> +	if (retval)
> +		return retval;
>  
>  	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
>  	if (filp->f_flags & O_DIRECT) {
> @@ -2094,30 +2112,14 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
>  	size_t ocount;		/* original count */
>  	size_t count;		/* after file limit checks */
>  	struct inode 	*inode = mapping->host;
> -	unsigned long	seg;
>  	loff_t		pos;
>  	ssize_t		written;
>  	ssize_t		err;
>  
>  	ocount = 0;
> -	for (seg = 0; seg < nr_segs; seg++) {
> -		const struct iovec *iv = &iov[seg];
> -
> -		/*
> -		 * If any segment has a negative length, or the cumulative
> -		 * length ever wraps negative then return -EINVAL.
> -		 */
> -		ocount += iv->iov_len;
> -		if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
> -			return -EINVAL;
> -		if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
> -			continue;
> -		if (seg == 0)
> -			return -EFAULT;
> -		nr_segs = seg;
> -		ocount -= iv->iov_len;	/* This segment is no good */
> -		break;
> -	}
> +	err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
> +	if (err)
> +		return err;
>  
>  	count = ocount;
>  	pos = *ppos;
> -- 
> 1.5.0.1
>