logging: Avoid memcpy from stack to msgb in _file_output()

For file and stderr output, the existing code always generates
the log string on a stack buffer, and then (in case of non-blocking
write via write_queue) copies it over to a msgb.

Let's optimize this by turning _file_output() into a raw_output
callback which first allocates the msgb and then format-prints
directly to that msgb instaed of stack + memcpy.

This has the disadvantage that we don't know how long the buffer
has to be in order to print the entire string to it.  As a result
we always have to allocate a 4k-sized buffer (plus msgb overhead).

The write_queue length for log file output has been decreased from
1024 entries to 156 entries in order to stay within the same
memory requirements for each log target memory pool (about 648 kBytes).

Related: OS#4311
Change-Id: I0d10b0199576d2e7ff6421a6dba19ae5ffafd946

0 files changed, 0 insertions, 0 deletions