Hello,
In a previous job, an engineer in our storage group modified our I/O stack logs
in a manner similar to your proposal #1 (except he did not tell anyone, and did
it for DEBUG messages as well as ERRORS and WARNINGS, over the weekend).
Developers came to work Monday and found over a thousand log message strings
had been buried in a new header file, and any new logs required a new message
id, along with a new string entry in the header file.
This did render the code harder to read. The ensuing uproar closely mirrored
the arguments (1) and (2) you listed. Logs are like comments. If you move them
out of the source, the code is harder to follow. And you probably wan't fewer
message IDs than comments.
The developer retracted his work. After some debate, his V2 solution resembled
your "approach #2". Developers were once again free to use plain text strings
directly in logs, but the notion of "classes" (message ID) was kept. We allowed
multiple text strings to be used against a single class, and any new classes
went in a master header file. The "debug" message ID class was a general
purpose bucket and what most coders used day to day.
So basically, your email sounded very familiar to me and I think your proposal
#2 is on the right track.
Dan
----- Original Message -----
From: "Nithya Balachandran" <nbala...@redhat.com>
To: gluster-devel@gluster.org
Cc: "gluster-users" <gluster-us...@gluster.org>
Sent: Wednesday, April 30, 2014 3:06:26 AM
Subject: [Gluster-devel] GlusterFS and the logging framework
Hi,
I have attached some DHT files to demonstrate the 2 logging approaches. (*_1 is
the original approach, *_2 is the proposed approach).I personally think the 2
approach leads to better code readability and propose that we follow approach
2. Please let me know of any concerns with this.
To consolidate all the points raised in the earlier discussions:
What are we trying to solve?
Improving gluster logs to make end user debugging easier by providing a
sufficient information and a consistent logging mechanism and message format .
The new logging framework already logs the function name and line, msgid and
strerror, which improves the log messages and debug-ability. However, there are
some potential issues with the way it is getting used. Please note - there are
no changes being proposed to the underlying logging framework.
Current approach (approach 1):
Define message_ids for each log message (except Trace and Debug) and associate
both id and string with a msg_id macro
Replace all calls to gf_log with gf_msg passing in the message_id for the
message. This message_id will be printed as part of the log message.
Document each log string with details of what caused it/how to fix it.
Issues:
1. Code readability - It becomes difficult to figure out what the following is
actually printing and can cause issues with incorrect params being passed or
params being passed in the wrong order:
gf_msg ("dht", GF_LOG_ERROR, 0, dht_msg_23, param1, param2, param3);
2.Code Redundancy -multiple messages for the same thing differing in small
details can potentially use up a large chunk of allocated ids as well as making
it difficult for end users - they will need to search for multiple string
formats/msgids as they could all refer to more or less the same thing. For
example:
dht_msg_1 123, "Failed to get cached subvol for %s"
dht_msg_2 124, "Failed to get cached subvol for %s on %s"
3. Documentation redundancy -
The proposed format for documenting these messages is as follows:
Msg ID
Message format string
Cause
Recommended action
This could potentially lead to documentation like:
Msg ID : 123
Message format string : Failed to get cached subvol for <path>
Cause : The subvolume might not be reachable etc etc
Recommended action : Check network connection etc etc
Msg ID : 124
Message format string : Failed to get cached subvol for <path> on <path2>
Cause : The subvolume might not be reachable etc etc
Recommended action : Check network connection etc etc
The end user now has to search for multiple msgids and string formats to find
all instances of this error.
NOTE: It may be possible to consolidate all these strings into a single one,
say, "Failed to get cached subvol for %s on %s" and mandate that it be used in
all calls which are currently using variations of the string. However, this
might not be possible in all scenarios - some params might not be available or
might not be meaningful in a particular case or a developer might want to
provide additional info in a particular scenario.
Proposed approach (approach 2):
Define meaningful macros for message_ids for a class of message (except Trace
and Debug) without associating them to a message string. For example
#define DHT_CACHED_SUBVOL_GET_FAILED 123
#define DHT_MEM_ALLOC_FAILED 124
Replace all calls to gf_log with gf_msg but pass in the msg id and string
separately. The string is defined by the developer based on an agreed upon
format.
Define a log message format policy that all developers need to follow. This
will need to be enforced by reviews. For example, we could mandate that all log
messages must start with the name of the file on which the operation is
performed and end with the strerror if it exists.This can also include rules as
to sentence structure and wording - whether to use "failed", "unable to",
"could not" etc.
Consolidate existing messages and reword them if necessary to make them more
meaningful. If a single message will work in multiple instances, use that one
everywhere.
Add your documentation writer as a reviewer for all patches. S/he will be
responsible for ensuring that all newly introduced log messages are meaningful,
consistent and follow the agreed upon format.
Devs will define new message classes ids as and when required.
Ideally, common message classes like dict-set-failed or memory-alloc-failed
should be defined in a common file and included by others - no point having
each component define a memory_alloc_failed id.
With the proposed approach:
#define DHT_CACHED_SUBVOL_GET_FAILED 123
#define DHT_HASHED_SUBVOL_GET_FAILED 124
Calls would then look like:
gf_msg ("dht", GF_LOG_ERROR, DHT_CACHED_SUBVOL_GET_FAILED, "Failed to get
cached subvolume for path %s", param1);
...
gf_msg ("dht", GF_LOG_ERROR, DHT_CACHED_SUBVOL_GET_FAILED, "Failed to get
cached subvolume for path %s on %s", param1, param2);
Documentation would be as follows:
Msg ID : 123
Description : Failed to get the cached subvolume for the specified path
Cause : The subvolume might not be reachable etc etc
Recommended action : Check network connection etc etc
Admins could just search for [MSGID 123] and find all instances of where an
operation failed to get a cached sub volume.
Issues raised with proposed approach:
1. Internationalization: Having the strings in a single file is required to
make L10N easy.
While i18n is very important for user tools, utils etc, log messages are
usually targeted at developers and sys admins who usually know English. Plus it
seems unlikely that log messages will be localized in the near future. However,
the document describing the msgid can be localized so the msg id mapping
information can still be used.
2. Having the strings in a header file makes it easier to change the format
later.
This is a valid point. However, IMHO, the code readability is more important
especially in the case where we pass arguments to the format string.
3. Having a string defined in a single header file can make it easier for a dev
to reuse it if necessary
I would suggest searching on the message id instead and copy the string from
elsewhere if it suits his purpose as those will already have been reviewed by
the doc writer.
Regards,
Nithya
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