Re: [f2fs-dev] [PATCH v2] libf2fs: don't allow mkfs / fsck on non power-of-2 zoned devices

From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Pankaj Raghav <p.raghav@samsung.com>
Cc: javier.gonz@samsung.com, Damien.LeMoal@wdc.com,
	mcgrof@kernel.org, pankydev8@gmail.com,
	linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] libf2fs: don't allow mkfs / fsck on non power-of-2 zoned devices
Date: Wed, 13 Apr 2022 12:45:55 -0700	[thread overview]
Message-ID: <Ylcoc0mfEIUS0e5Q@google.com> (raw)
In-Reply-To: <6f508044-5329-f864-3879-c42a59d52366@samsung.com>

On 04/13, Pankaj Raghav wrote:
> Hi Jaegeuk,
> 
> On 2022-04-13 19:03, Jaegeuk Kim wrote
> >> @@ -882,6 +882,11 @@ static int open_check_fs(char *path, int flag)
> >>  	return open(path, O_RDONLY | flag);
> >>  }
> >>  
> >> +static int is_power_of_2(unsigned long n)
> > 
> > So, this needs to check 2MB alignment only?
> > 
> As I explained in the v1 thread, zoned support for f2fs assumes po2 zone
> sizes. For e.g.,
> static int __f2fs_issue_discard_zone(struct f2fs_sb_info *sbi,
> 		struct block_device *bdev, block_t blkstart, block_t blklen)
> {
> 	sector_t sector, nr_sects;
> 	block_t lblkstart = blkstart;
> 	int devi = 0;
> ...
> ...
> 		// Assumes zone sectors to be po2

Well, I think this will be aligned to 2MB, if the device gives NPO2? IOWs, this
is just checking the granularity, not PO2.

> 		if (sector & (bdev_zone_sectors(bdev) - 1) ||
> 				nr_sects != bdev_zone_sectors(bdev)) {
> 			f2fs_err(sbi, "(%d) %s: Unaligned zone reset attempted (block %x + %x)",
> 				 devi, sbi->s_ndevs ? FDEV(devi).path : "",
> 				 blkstart, blklen);
> 			return -EIO;
> 		}
> 
> ...
> }
> 
> So until non power of 2 zoned devices are supported in block layer and
> f2fs, it is safer to reject non power of 2 devices during mkfs time. I
> hope it clarifies.

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