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List:       linux-btrfs
Subject:    Re: [PATCH 1/2] btrfs-progs: raid56: Add support for raid5 to calculate any stripe
From:       Qu Wenruo <quwenruo () cn ! fujitsu ! com>
Date:       2016-09-30 0:49:59
Message-ID: aed84e6d-35ef-5907-9c3d-f13f65be7cf9 () cn ! fujitsu ! com
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At 09/30/2016 01:37 AM, David Sterba wrote:
> On Wed, Sep 28, 2016 at 04:30:03PM +0800, Qu Wenruo wrote:
>> Add a new function raid5_gen_result() to calculate raid5 parity or
>> recover data stripe.
>>
>> Since now that raid6.c handles both raid5 and raid6, rename it to
>> raid56.c.
>
> Please split changes in this patch to the following:
> - rename the file
> - error handling of memory allocation failures
> - the actual fix
>
> A test would be very velcome, for all the cases the code handles, 2
> devices, and more. But I'm not sure if we have support for that in the
> testing suite.

Makes sense.

I'll split first and try if I can create some test cases for RAID5/6 codes.

But the later work may be delayed since I'm working on user-space scrub.
(Which will lead to kernel scrub fix).

Thanks,
Qu

>
>> @@ -107,3 +108,47 @@ void raid6_gen_syndrome(int disks, size_t bytes, void **ptrs)
>>  	}
>>  }
>>
>> +static void xor_range(void *src, void *dst, size_t size)
>> +{
>> +	while (size) {
>> +		*(unsigned long *) dst ^= *(unsigned long *) src;
>
> This could lead to unaligned access, please update the types and
> possibly add some sanity checks (alignemnt, length).
>
>> +		src += sizeof(unsigned long);
>> +		dst += sizeof(unsigned long);
>> +		size -= sizeof(unsigned long);
>> +	}
>> +}
>> +
>> +/*
>> + * Generate desired data/parity for RAID5
>> + *
>> + * @nr_devs:	Total number of devices, including parity
>> + * @stripe_len:	Stripe length
>> + * @data:	Data, with special layout:
>> + * 		data[0]:	 Data stripe 0
>> + * 		data[nr_devs-2]: Last data stripe
>> + * 		data[nr_devs-1]: RAID5 parity
>> + * @dest:	To generate which data. should follow above data layout
>> + */
>> +int raid5_gen_result(int nr_devs, size_t stripe_len, int dest, void **data)
>> +{
>> +	int i;
>> +	char *buf = data[dest];
>> +
>> +	if (dest >= nr_devs || nr_devs < 2) {
>> +		error("invalid parameter for %s", __func__);
>> +		return -EINVAL;
>> +	}
>> +	/* Quich hack, 2 devs RAID5 is just RAID1, no need to calculate */
>
> This is not a hack IMO, it could be a shortcut, a special case, an
> optimization.
>
>> +	if (nr_devs == 2) {
>> +		memcpy(data[dest], data[1 - dest], stripe_len);
>> +		return 0;
>> +	}
>> +	/* Just in case */
>
> Such comment is not very helpful.
>
>> +	memset(buf, 0, stripe_len);
>> +	for (i = 0; i < nr_devs; i++) {
>> +		if (i == dest)
>> +			continue;
>> +		xor_range(data[i], buf, stripe_len);
>> +	}
>> +	return 0;
>> +}
>> diff --git a/volumes.c b/volumes.c
>> index da79751..718e67c 100644
>> --- a/volumes.c
>> +++ b/volumes.c
>> @@ -2108,12 +2108,14 @@ int write_raid56_with_parity(struct btrfs_fs_info *info,
>>  {
>>  	struct extent_buffer **ebs, *p_eb = NULL, *q_eb = NULL;
>>  	int i;
>> -	int j;
>>  	int ret;
>>  	int alloc_size = eb->len;
>> +	void **pointers;
>
> I see you're moving existing code, so if you're going to fix the types,
> please do that in a separate patch as well.
>
>> -	ebs = kmalloc(sizeof(*ebs) * multi->num_stripes, GFP_NOFS);
>> -	BUG_ON(!ebs);
>> +	ebs = malloc(sizeof(*ebs) * multi->num_stripes);
>> +	pointers = malloc(sizeof(void *) * multi->num_stripes);
>> +	if (!ebs || !pointers)
>> +		return -ENOMEM;
>>
>>  	if (stripe_len > alloc_size)
>>  		alloc_size = stripe_len;
>> @@ -2143,12 +2145,6 @@ int write_raid56_with_parity(struct btrfs_fs_info *info,
>>  			q_eb = new_eb;
>>  	}
>>  	if (q_eb) {
>> -		void **pointers;
>> -
>> -		pointers = kmalloc(sizeof(*pointers) * multi->num_stripes,
>> -				   GFP_NOFS);
>> -		BUG_ON(!pointers);
>> -
>>  		ebs[multi->num_stripes - 2] = p_eb;
>>  		ebs[multi->num_stripes - 1] = q_eb;
>>
>> @@ -2159,17 +2155,14 @@ int write_raid56_with_parity(struct btrfs_fs_info *info,
>>  		kfree(pointers);
>>  	} else {
>>  		ebs[multi->num_stripes - 1] = p_eb;
>> -		memcpy(p_eb->data, ebs[0]->data, stripe_len);
>> -		for (j = 1; j < multi->num_stripes - 1; j++) {
>> -			for (i = 0; i < stripe_len; i += sizeof(u64)) {
>> -				u64 p_eb_data;
>> -				u64 ebs_data;
>> -
>> -				p_eb_data = get_unaligned_64(p_eb->data + i);
>> -				ebs_data = get_unaligned_64(ebs[j]->data + i);
>> -				p_eb_data ^= ebs_data;
>> -				put_unaligned_64(p_eb_data, p_eb->data + i);
>> -			}
>> +		for (i = 0; i < multi->num_stripes; i++)
>> +			pointers[i] = ebs[i]->data;
>> +		ret = raid5_gen_result(multi->num_stripes, stripe_len,
>> +				multi->num_stripes - 1, pointers);
>> +		if (ret < 0) {
>> +			free(ebs);
>> +			free(pointers);
>> +			return ret;
>>  		}
>>  	}
>>
>> @@ -2180,7 +2173,8 @@ int write_raid56_with_parity(struct btrfs_fs_info *info,
>>  			kfree(ebs[i]);
>>  	}
>>
>> -	kfree(ebs);
>> +	free(ebs);
>> +	free(pointers);
>>
>>  	return 0;
>
>


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