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Document guidelines for usage of zfs_dbgmsg 

Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8299
This commit is contained in:
Serapheim Dimitropoulos 2019-01-18 10:16:56 -08:00 committed by Brian Behlendorf
parent e45c1734a6
commit 1a759200e5
1 changed files with 17 additions and 1 deletions
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18
include/sys/zfs_debug.h
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@ -20,7 +20,7 @@
*/
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
*/
#ifndef _SYS_ZFS_DEBUG_H
@ -58,6 +58,22 @@ extern int zfs_dbgmsg_enable;
extern void __zfs_dbgmsg(char *buf);
extern void __dprintf(boolean_t dprint, const char *file, const char *func,
int line, const char *fmt, ...);
/*
* Some general principles for using zfs_dbgmsg():
* 1. We don't want to pollute the log with typically-irrelevant messages,
* so don't print too many messages in the "normal" code path - O(1)
* per txg.
* 2. We want to know for sure what happened, so make the message specific
* (e.g. *which* thing am I operating on).
* 3. Do print a message when something unusual or unexpected happens
* (e.g. error cases).
* 4. Print a message when making user-initiated on-disk changes.
*
* Note that besides principle 1, another reason that we don't want to
* use zfs_dbgmsg in high-frequency routines is the potential impact
* that it can have on performance.
*/
#define zfs_dbgmsg(...) \
if (zfs_dbgmsg_enable) \
__dprintf(B_FALSE, __FILE__, __func__, __LINE__, __VA_ARGS__)