linux-ext4 - Re: [PATCH] ext4: Don't report EOPNOTSUPP errors from discard

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Message-Id: <4AC7AEC3-25FC-4147-9C62-2CE5A1686199@dilger.ca>
Date: Wed, 14 Feb 2024 16:01:57 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: Jan Kara <jack@...e.cz>
Cc: Ted Tso <tytso@....edu>,
 linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Don't report EOPNOTSUPP errors from discard

On Feb 13, 2024, at 3:16 AM, Jan Kara <jack@...e.cz> wrote:
> 
> When ext4 is mounted without journal, with discard mount option, and on
> a device not supporting trim, we print error for each and every freed
> extent. This is not only useless but actively harmful. Instead ignore
> the EOPNOTSUPP error. Trim is only advisory anyway and when the
> filesystem has journal we silently ignore trim error as well.
> 

> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
> fs/ext4/mballoc.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index e4f7cf9d89c4..aed620cf4d40 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -6488,7 +6488,13 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
> 		if (test_opt(sb, DISCARD)) {
> 			err = ext4_issue_discard(sb, block_group, bit,
> 						 count_clusters, NULL);
> -			if (err && err != -EOPNOTSUPP)
> +			/*
> +			 * Ignore EOPNOTSUPP error. This is consistent with
> +			 * what happens when using journal.
> +			 */
> +			if (err == -EOPNOTSUPP)
> +				err = 0;
> +			if (err)

I don't see how this patch is actually changing whether the error message
is printed?  Previously, if "err" was set and err was -EOPNOTSUPP the
message was skipped.  Now it is doing the same thing in a different way?

The "err" value is overwritten 50 lines later on without being used:

        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);

so the setting "err = 0" doesn't really affect the later code either.
What am I missing?

Cheers, Andreas



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