linux-kernel - Re: [PATCH v11 7/8] xfs: Implement ->notify

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Message-ID: <894ed00b-b174-6a10-ee45-320007957ea4@fujitsu.com>
Date:   Wed, 30 Mar 2022 23:16:10 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
        <nvdimm@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <djwong@...nel.org>,
        <dan.j.williams@...el.com>, <david@...morbit.com>,
        <jane.chu@...cle.com>
Subject: Re: [PATCH v11 7/8] xfs: Implement ->notify_failure() for XFS



在 2022/3/30 14:00, Christoph Hellwig 写道:
>> @@ -1892,6 +1893,8 @@ xfs_free_buftarg(
>>   	list_lru_destroy(&btp->bt_lru);
>>   
>>   	blkdev_issue_flush(btp->bt_bdev);
>> +	if (btp->bt_daxdev)
>> +		dax_unregister_holder(btp->bt_daxdev, btp->bt_mount);
>>   	fs_put_dax(btp->bt_daxdev);
>>   
>>   	kmem_free(btp);
>> @@ -1939,6 +1942,7 @@ xfs_alloc_buftarg(
>>   	struct block_device	*bdev)
>>   {
>>   	xfs_buftarg_t		*btp;
>> +	int			error;
>>   
>>   	btp = kmem_zalloc(sizeof(*btp), KM_NOFS);
>>   
>> @@ -1946,6 +1950,14 @@ xfs_alloc_buftarg(
>>   	btp->bt_dev =  bdev->bd_dev;
>>   	btp->bt_bdev = bdev;
>>   	btp->bt_daxdev = fs_dax_get_by_bdev(bdev, &btp->bt_dax_part_off);
>> +	if (btp->bt_daxdev) {
>> +		error = dax_register_holder(btp->bt_daxdev, mp,
>> +				&xfs_dax_holder_operations);
>> +		if (error) {
>> +			xfs_err(mp, "DAX device already in use?!");
>> +			goto error_free;
>> +		}
>> +	}
> 
> It seems to me that just passing the holder and holder ops to
> fs_dax_get_by_bdev and the holder to dax_unregister_holder would
> significantly simply the interface here.
> 
> Dan, what do you think?
> 
>> +#if IS_ENABLED(CONFIG_MEMORY_FAILURE) && IS_ENABLED(CONFIG_FS_DAX)
> 
> No real need for the IS_ENABLED.  Also any reason to even build this
> file if the options are not set?  It seems like
> xfs_dax_holder_operations should just be defined to NULL and the
> whole file not supported if we can't support the functionality.

Got it.  These two CONFIG seem not related for now.  So, I think I 
should wrap these code with #ifdef CONFIG_MEMORY_FAILURE here, and add 
`xfs-$(CONFIG_FS_DAX) += xfs_notify_failure.o` in the makefile.

> 
> Dan: not for this series, but is there any reason not to require
> MEMORY_FAILURE for DAX to start with?
> 
>> +
>> +	ddev_start = mp->m_ddev_targp->bt_dax_part_off;
>> +	ddev_end = ddev_start +
>> +		(mp->m_ddev_targp->bt_bdev->bd_nr_sectors << SECTOR_SHIFT) - 1;
> 
> This should use bdev_nr_bytes.

OK.

> 
> But didn't we say we don't want to support notifications on partitioned
> devices and thus don't actually need all this?
> 
>> +
>> +	/* Ignore the range out of filesystem area */
>> +	if ((offset + len) < ddev_start)
> 
> No need for the inner braces.
> 
>> +	if ((offset + len) > ddev_end)
> 
> No need for the braces either.

Really no need?  It is to make sure the range to be handled won't out of 
the filesystem area.  And make sure the @offset and @len are valid and 
correct after subtract the bbdev_start.

> 
>> diff --git a/fs/xfs/xfs_notify_failure.h b/fs/xfs/xfs_notify_failure.h
>> new file mode 100644
>> index 000000000000..76187b9620f9
>> --- /dev/null
>> +++ b/fs/xfs/xfs_notify_failure.h
>> @@ -0,0 +1,10 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2022 Fujitsu.  All Rights Reserved.
>> + */
>> +#ifndef __XFS_NOTIFY_FAILURE_H__
>> +#define __XFS_NOTIFY_FAILURE_H__
>> +
>> +extern const struct dax_holder_operations xfs_dax_holder_operations;
>> +
>> +#endif  /* __XFS_NOTIFY_FAILURE_H__ */
> 
> Dowe really need a new header for this vs just sequeezing it into
> xfs_super.h or something like that?

Yes, I'll move it into xfs_super.h.  The xfs_notify_failure.c was 
splitted from xfs_super.c in the old patch.  There is no need to create 
a header file for only single line of code.

> 
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index e8f37bdc8354..b8de6ed2c888 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -353,6 +353,12 @@ xfs_setup_dax_always(
>>   		return -EINVAL;
>>   	}
>>   
>> +	if (xfs_has_reflink(mp) && !xfs_has_rmapbt(mp)) {
>> +		xfs_alert(mp,
>> +			"need rmapbt when both DAX and reflink enabled.");
>> +		return -EINVAL;
>> +	}
> 
> Right now we can't even enable reflink with DAX yet, so adding this
> here seems premature - it should go into the patch allowing DAX+reflink.
> 

Yes.  I'll remove it for now.


--
Thanks,
Ruan.