linux-ext4 - Re: [PATCH] ext4: remove EXT4_EOFBLOCKS

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Message-ID: <20200305205724.GE20967@mit.edu>
Date:   Thu, 5 Mar 2020 15:57:24 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Whitney <enwlinux@...il.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: remove EXT4_EOFBLOCKS_FL and associated code

On Tue, Feb 11, 2020 at 04:02:16PM -0500, Eric Whitney wrote:
> The EXT4_EOFBLOCKS_FL inode flag is used to indicate whether a file
> contains unwritten blocks past i_size.  It's set when ext4_fallocate
> is called with the KEEP_SIZE flag to extend a file with an unwritten
> extent.  However, this flag hasn't been useful functionally since
> March, 2012, when a decision was made to remove it from ext4.
> 
> All traces of EXT4_EOFBLOCKS_FL were removed from e2fsprogs version
> 1.42.2 by commit 010dc7b90d97 ("e2fsck: remove EXT4_EOFBLOCKS_FL flag
> handling") at that time.  Now that enough time has passed to make
> e2fsprogs versions containing this modification common, this patch now
> removes the code associated with EXT4_EOFBLOCKS_FL from the kernel as
> well.
> 
> This change has two implications.  First, because pre-1.42.2 e2fsck
> versions only look for a problem if EXT4_EOFBLOCKS_FL is set, and
> because that bit will never be set by newer kernels containing this
> patch, old versions of e2fsck won't have a compatibility problem with
> files created by newer kernels.
> 
> Second, newer kernels will not clear EXT4_EOFBLOCKS_FL inode flag bits
> belonging to a file written by an older kernel.  If set, it will remain
> in that state until the file is deleted.  Because e2fsck versions since
> 1.42.2 don't check the flag at all, no adverse effect is expected.
> However, pre-1.42.2 e2fsck versions that do check the flag may report
> that it is set when it ought not to be after a file has been truncated
> or had its unwritten blocks written.  In this case, the old version of
> e2fsck will offer to clear the flag.  No adverse effect would then
> occur whether the user chooses to clear the flag or not.
> 
> Signed-off-by: Eric Whitney <enwlinux@...il.com>

Applied, thanks.

							- Ted