Re: [RFC 9/9] __xfs_printk: Add durable name to output

[Tony Asleson <tasleson@redhat.com>]

On 1/3/20 8:56 PM, Dave Chinner wrote:
> On Mon, Dec 23, 2019 at 04:55:58PM -0600, Tony Asleson wrote:
>> Add persistent durable name to xfs messages so we can
>> correlate them with other messages for the same block
>> device.
>>
>> Signed-off-by: Tony Asleson <tasleson@redhat.com>
>> ---
>>  fs/xfs/xfs_message.c | 17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_message.c b/fs/xfs/xfs_message.c
>> index 9804efe525a9..8447cdd985b4 100644
>> --- a/fs/xfs/xfs_message.c
>> +++ b/fs/xfs/xfs_message.c
>> @@ -20,6 +20,23 @@ __xfs_printk(
>>  	const struct xfs_mount	*mp,
>>  	struct va_format	*vaf)
>>  {
>> +	char dict[128];
>> +	int dict_len = 0;
>> +
>> +	if (mp && mp->m_super && mp->m_super->s_bdev &&
>> +		mp->m_super->s_bdev->bd_disk) {
>> +		dict_len = dev_durable_name(
>> +			disk_to_dev(mp->m_super->s_bdev->bd_disk)->parent,
>> +			dict,
>> +			sizeof(dict));
>> +		if (dict_len) {
>> +			printk_emit(
>> +				0, level[1] - '0', dict, dict_len,
>> +				"XFS (%s): %pV\n",  mp->m_fsname, vaf);
>> +			return;
>> +		}
>> +	}
> 
> NACK on the ground this is a gross hack.

James suggested I utilize dev_printk, which does make things simpler.
Would something like this be acceptable?

diff --git a/fs/xfs/xfs_message.c b/fs/xfs/xfs_message.c
index 9804efe525a9..0738c74a8d3a 100644
--- a/fs/xfs/xfs_message.c
+++ b/fs/xfs/xfs_message.c
@@ -20,11 +20,18 @@ __xfs_printk(
        const struct xfs_mount  *mp,
        struct va_format        *vaf)
 {
+       struct device *dev = NULL;
+
+       if (mp && mp->m_super && mp->m_super->s_bdev &&
+               mp->m_super->s_bdev->bd_disk) {
+               dev = disk_to_dev(mp->m_super->s_bdev->bd_disk)->parent;
+       }
+
        if (mp && mp->m_fsname) {
-               printk("%sXFS (%s): %pV\n", level, mp->m_fsname, vaf);
+               dev_printk(level, dev, "XFS (%s): %pV\n", mp->m_fsname,
vaf);
                return;
        }
-       printk("%sXFS: %pV\n", level, vaf);
+       dev_printk(level, dev, "XFS: %pV\n", vaf);
 }

>> +
>>  	if (mp && mp->m_fsname) {
> 
> mp->m_fsname is the name of the device we use everywhere for log
> messages, it's set up at mount time so we don't have to do runtime
> evaulation of the device name every time we need to emit the device
> name in a log message.
> 
> So, if you have some sooper speshial new device naming scheme, it
> needs to be stored into the struct xfs_mount to replace mp->m_fsname.

I don't think we want to replace mp->m_fsname with the vpd 0x83 device
identifier.  This proposed change is adding a key/value structured data
to the log message for non-ambiguous device identification over time,
not to place the ID in the human readable portion of the message.  The
existing name is useful too, especially when it involves a partition.

> And if you have some sooper spehsial new printk API that uses this
> new device name, everything XFS emits needs to use it
> unconditionally as we do with mp->m_fsname now.
> 
> IOWs, this isn't conditional code - it either works for the entire
> life of the mount for every message we have to emit with a single
> setup call, or the API is broken and needs to be rethought.

I've been wondering why the struct scsi device uses rcu data for the vpd
as I would not think that it would be changing for a specific device.
Perhaps James can shed some light on this?

-Tony