linux-kernel - Re: [PATCH v2] btrfs: add fs state details to error messages.

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Message-ID: <20220221163808.GI12643@twin.jikos.cz>
Date:   Mon, 21 Feb 2022 17:38:08 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Sweet Tea Dorminy <sweettea-kernel@...miny.me>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v2] btrfs: add fs state details to error messages.

On Fri, Feb 18, 2022 at 02:04:29PM -0500, Sweet Tea Dorminy wrote:
> When a filesystem goes read-only due to an error, multiple errors tend
> to be reported, some of which are knock-on failures. Logging some
> fs_states, if any, in btrfs_handle_fs_error() and btrfs_printk()
> helps distinguish the first error from subsequent messages which may
> only exist due to an error state.
> 
> Under the new format, most initial errors will look like:
> `BTRFS: error (device loop0) in ...`
> while subsequent errors will begin with:
> `error (device loop0: state E) in ...`
> 
> An initial transaction abort error will look like
> `error (device loop0: state X) in ...`
> and subsequent messages will contain
> `(device loop0: state EX) in ...`

I think there should be also BTRFS_FS_STATE_LOG_CLEANUP_ERROR, and the
letter maybe more hinting of the error:

E - generic error
A - transaction abort
L - log related errors

> 
> Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@...miny.me>
> ---
> v2:
>   - Changed btrfs_state_to_string() for clarity
>   - Removed superfluous whitespace change
> 
> v1:
>   - https://lore.kernel.org/linux-btrfs/20220212191042.94954-1-sweettea-kernel@dorminy.me/
> 
>  fs/btrfs/super.c | 53 ++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 45 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 4d947ba32da9..42429d68950d 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -66,6 +66,37 @@ static struct file_system_type btrfs_root_fs_type;
>  
>  static int btrfs_remount(struct super_block *sb, int *flags, char *data);
>  
> +#define STATE_STRING_PREFACE ": state "
> +#define MAX_STATE_CHARS 2
> +
> +static void btrfs_state_to_string(const struct btrfs_fs_info *info, char *buf)
> +{
> +	unsigned int states_printed = 0;
> +	char *curr = buf;
> +
> +	memcpy(curr, STATE_STRING_PREFACE, sizeof(STATE_STRING_PREFACE));
> +	curr += sizeof(STATE_STRING_PREFACE) - 1;
> +
> +	/* If more states are reported, update MAX_STATE_CHARS also */
> +	if (test_bit(BTRFS_FS_STATE_ERROR, &info->fs_state)) {
> +		*curr++ = 'E';
> +		states_printed++;
> +	}
> +
> +	if (test_bit(BTRFS_FS_STATE_TRANS_ABORTED, &info->fs_state)) {
> +		*curr++ = 'X';
> +		states_printed++;
> +	}
> +

So if we have more than 2 it may make sense to create a table and not to
opencode it like that and then use the constants (MAX_STATE_CHARS)
everywhere. For first implementation it's probably ok to have it like
three ifs.

> +	/* If no states were printed, reset the buffer */
> +	if (!states_printed)
> +		curr = buf;
> +
> +	WARN_ON_ONCE(states_printed > MAX_STATE_CHARS);
> +
> +	*curr++ = '\0';
> +}
> +
>  /*
>   * Generally the error codes correspond to their respective errors, but there
>   * are a few special cases.
> @@ -128,6 +159,7 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
>  {
>  	struct super_block *sb = fs_info->sb;
>  #ifdef CONFIG_PRINTK
> +	char statestr[sizeof(STATE_STRING_PREFACE) + MAX_STATE_CHARS];

A size defintion like that could be also predefined.

>  	const char *errstr;
>  #endif
>  
> @@ -140,6 +172,7 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
>  
>  #ifdef CONFIG_PRINTK
>  	errstr = btrfs_decode_error(errno);
> +	btrfs_state_to_string(fs_info, statestr);
>  	if (fmt) {
>  		struct va_format vaf;
>  		va_list args;
> @@ -148,12 +181,12 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
>  		vaf.fmt = fmt;
>  		vaf.va = &args;
>  
> -		pr_crit("BTRFS: error (device %s) in %s:%d: errno=%d %s (%pV)\n",
> -			sb->s_id, function, line, errno, errstr, &vaf);
> +		pr_crit("BTRFS: error (device %s%s) in %s:%d: errno=%d %s (%pV)\n",
> +			sb->s_id, statestr, function, line, errno, errstr, &vaf);
>  		va_end(args);
>  	} else {
> -		pr_crit("BTRFS: error (device %s) in %s:%d: errno=%d %s\n",
> -			sb->s_id, function, line, errno, errstr);
> +		pr_crit("BTRFS: error (device %s%s) in %s:%d: errno=%d %s\n",
> +			sb->s_id, statestr, function, line, errno, errstr);
>  	}
>  #endif
>  
> @@ -240,11 +273,15 @@ void __cold btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, .
>  	vaf.va = &args;
>  
>  	if (__ratelimit(ratelimit)) {
> -		if (fs_info)
> -			printk("%sBTRFS %s (device %s): %pV\n", lvl, type,
> -				fs_info->sb->s_id, &vaf);
> -		else
> +		if (fs_info) {
> +			char statestr[sizeof(STATE_STRING_PREFACE) + MAX_STATE_CHARS];
> +
> +			btrfs_state_to_string(fs_info, statestr);
> +			printk("%sBTRFS %s (device %s%s): %pV\n", lvl, type,
> +				fs_info->sb->s_id, statestr, &vaf);
> +		} else {
>  			printk("%sBTRFS %s: %pV\n", lvl, type, &vaf);
> +		}
>  	}
>  
>  	va_end(args);
> -- 
> 2.35.1