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

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Date:	Mon, 12 Mar 2007 21:32:28 +0300
From:	Dmitriy Monakhov <dmonakhov@...ru>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Dmitriy Monakhov <dmonakhov@...ru>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, devel@...nvz.org
Subject: Re: [PATCH 1/2] mm: move common segment checks to separate helper function (v6)

Nick Piggin <npiggin@...e.de> writes:

> 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.

>> +/*
>> + * 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.
Wow i've just carefully checked and found more functions with duplicating code:
fs/xfs/linux-2.6/xfs_lrw.c:655 xfs_write()
fs/ntfs/file.c:2339 ntfs_file_aio_write_nolock()
So i think nobody will object against exporting generic_segment_checks()
and removing doplicating code.
>
> 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
>> 
> -
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