[PATCH net-next 0/9] netconsole refactoring and warning fix

Breno Leitao
2024-09-03T14:08:04Z

The netconsole driver was showing a warning related to userdata
information, depending on the message size being transmitted:

------------[ cut here ]------------
WARNING: CPU: 13 PID: 3013042 at drivers/net/netconsole.c:1122 write_ext_msg+0x3b6/0x3d0
? write_ext_msg+0x3b6/0x3d0
console_flush_all+0x1e9/0x330
...

Identifying the cause of this warning proved to be non-trivial due to:

* The write_ext_msg() function being over 100 lines long
* Extensive use of pointer arithmetic
* Inconsistent naming conventions and concept application

The send_ext_msg() function grew organically over time:

* Initially, the UDP packet consisted of a header and body
* Later additions included release prepend and userdata
* Naming became inconsistent (e.g., "body" excludes userdata, "header"
excludes prepended release)

This lack of consistency made investigating issues like the above warning
more challenging than what it should be.

To address these issues, the following steps were taken:

* Breaking down write_ext_msg() into smaller functions with clear scopes
* Improving readability and reasoning about the code
* Simplifying and clarifying naming conventions

Warning Fix
-----------

The warning occurred when there was insufficient buffer space to append
userdata. While this scenario is acceptable (as userdata can be sent in a
separate packet later), the kernel was incorrectly raising a warning. A
one-line fix has been implemented to resolve this issue.

A self-test was developed to write messages of every possible length
This test will be submitted in a separate patchset

Breno Leitao (9):
net: netconsole: remove msg_ready variable
net: netconsole: split send_ext_msg_udp() function
net: netconsole: separate fragmented message handling in send_ext_msg
net: netconsole: rename body to msg_body
net: netconsole: introduce variable to track body length
net: netconsole: track explicitly if msgbody was written to buffer
net: netconsole: extract release appending into separate function
net: netconsole: split send_msg_fragmented
net: netconsole: fix a wrong warning

drivers/net/netconsole.c | 207 +++++++++++++++++++++++++--------------
1 file changed, 134 insertions(+), 73 deletions(-)

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2.43.5