In general we almost never hit those asserts in production code, so users see
them very rarely, if ever. But either way, we just need something that users
can pass to the developers.
We have quite a few of those asserts, and some have fairly nice messages, but
many are like "WTF?" or "???" or "unexpected something". The error that is
printed includes the file location, and function name. In almost all functions
there's at most one assert, so the function name alone is enough to identify
the failure for a developer. So we don't get much extra from the message, and
we might just as well drop them.
Dropping them makes our code a tiny bit smaller, and most importantly, improves
development experience by making it easy to insert such an assert in the code
without thinking how to phrase the argument.
We recently started making more use of malloc_usable_size() and rely on
it (see the string_erase() story). Given that we don't really support
sytems where malloc_usable_size() cannot be trusted beyond statistics
anyway, let's go fully in and rework GREEDY_REALLOC() on top of it:
instead of passing around and maintaining the currenly allocated size
everywhere, let's just derive it automatically from
malloc_usable_size().
I am mostly after this for the simplicity this brings. It also brings
minor efficiency improvements I guess, but things become so much nicer
to look at if we can avoid these allocation size variables everywhere.
Note that the malloc_usable_size() man page says relying on it wasn't
"good programming practice", but I think it does this for reasons that
don't apply here: the greedy realloc logic specifically doesn't rely on
the returned extra size, beyond the fact that it is equal or larger than
what was requested.
(This commit was supposed to be a quick patch btw, but apparently we use
the greedy realloc stuff quite a bit across the codebase, so this ends
up touching *a*lot* of code.)
With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.
gcc 9.3.0 "cc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0" with --optimization=1 was
not able to figure out that all cases are covered because r is either set in
the switch or type < _TABLE_DATA_TYPE_MAX.
But for a human reader this might also not be obvious: the cases are not in
exactly the same order as enum definitions, and it's a long list. By using the
goto, there should be no doubt, and we avoid checking the condition a second
time.
This way we can display invalid UIDs/GIDs/PIDs as n/a while still
storing them as is.
Also, let's add a new cell type for unix signal, that is stored as
integer, but displayed as signal name string.
If one field in a specific column has a maximum size limit, other fields
in the same column might affected by it and get less than they asked
for. Let's make sure we can handle this, and don't assert on this
because surprisingly we got less than what we asked for.
This adds a new function table_print_with_pager() which is a wrapper
around table_print_json()/table_print() but spawns a pager first, if
that's enabled, and optionally turns off the header line of the table.
This addresses the fact that many of our tools actually keep doing very
this very similar stuff, over and over again. Let's unify this in one
place.
This adds a new flag JSON_FORMAT_OFF that is a marker for "no JSON
output please!".
Of course, this flag sounds pointless in a JSON implementation, however
this is useful in code that can generate JSON output, but also more
human friendly output (for example our table formatters).
With this in place various tools that so far maintained one boolean
field "arg_json" that controlled whether JSON output was requested at
all and another field "arg_json_format_flags" for selecing the precise
json output flags may merge them into one, simplifying code a bit.
The idea is that we have strvs like list of server names or addresses, where
the majority of strings is rather short, but some are long and there can
potentially be many strings. So formattting them either all on one line or all
in separate lines leads to output that is either hard to read or uses way too
many rows. We want to wrap them, but relying on the pager to do the wrapping is
not nice. Normal text has a lot of redundancy, so when the pager wraps a line
in the middle of a word the read can understand what is going on without any
trouble. But for a high-density zero-redundancy text like an IP address it is
much nicer to wrap between words. This also makes c&p easier.
This adds a variant of TABLE_STRV which is wrapped on output (with line breaks
inserted between different strv entries).
The change table_print() is quite ugly. A second pass is added to re-calculate
column widths. Since column size is now "soft", i.e. it can adjust based on
available columns, we need to two passes:
- first we figure out how much space we want
- in the second pass we figure out what the actual wrapped columns
widths will be.
To avoid unnessary work, the second pass is only done when we actually have
wrappable fields.
A test is added in test-format-table.
Let's try to mangle table contents a bit to make them more suitable as
JSON field names. Specifically when we see "foo bar" convert this to
"foo_bar" as field name, as variable/field names are generally assumed
to be without spaces.
Lennart Poettering
Zbigniew Jędrzejewski-Szmek
Yu Watanabe
Luca Boccassi
наб
Frantisek Sumsal