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

Tony Asleson
2020-01-06T02:45:13Z

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