linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: change the way of handling range.len in F2FS_IOC_SEC_TRIM

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Date:   Thu, 9 Jul 2020 20:25:31 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Daeho Jeong <daeho43@...il.com>,
        Daeho Jeong <daehojeong@...gle.com>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: change the way of handling range.len in
 F2FS_IOC_SEC_TRIM_FILE

On Thu, Jul 09, 2020 at 08:20:35PM -0700, Jaegeuk Kim wrote:
> On 07/10, Daeho Jeong wrote:
> > 1. The valid data will be within i_size.
> > 2. All the trim operations will be done in a unit of block, even if
> > i_size is not aligned with BLKSIZE like the below.
> > 
> >         index = F2FS_BYTES_TO_BLK(range.start);
> >         pg_end = DIV_ROUND_UP(end_addr, F2FS_BLKSIZE);     <= BLKSIZE aligned
> > 
> > Are you worried about the case that sudden power-off occurs while a
> > file is being truncated?
> > ex) 1GB file is being truncated to 4KB -> sudden power-off ->
> > i_size(4KB), i_blocks(maybe somewhere between 4KB and 1GB)
> 
> Yes. Basically, I believe we can have some data beyond i_size like fsverity.
> 

Note that fs-verity files are read-only, and therefore this ioctl can't be used
on them (since it requires a writable file descriptor).  So that case doesn't
need to be handled here.

- Eric