Date: Tue, 7 Apr 2015 17:11:10 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Chris Torek <torek@torek.net> Cc: freebsd-arch@freebsd.org Subject: Re: sysctl output formatting Message-ID: <20150407144043.W1410@besplex.bde.org> In-Reply-To: <201504062229.t36MTMlJ024359@elf.torek.net> References: <201504062229.t36MTMlJ024359@elf.torek.net>
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On Mon, 6 Apr 2015, Chris Torek wrote:
> We had a side discussion at $work about a private sysctl emulation
> (so our side thing doesn't actually affect sysctl itself at all)
> where it was suggested that some simple numeric sysctls are "best
> displayed in hex".
>
> Consider, e.g.:
>
> $ sysctl kern.timecounter.tc.i8254
> kern.timecounter.tc.i8254.mask: 65535
> kern.timecounter.tc.i8254.counter: 25822
> kern.timecounter.tc.i8254.frequency: 1193182
> kern.timecounter.tc.i8254.quality: 0
>
> The "mask" here actually makes more sense displayed in hex. One
> can of course use:
>
> $ sysctl -x kern.timecounter.tc.i8254
> kern.timecounter.tc.i8254.mask: 0x0000ffff
> kern.timecounter.tc.i8254.counter: 0x0000786c
> kern.timecounter.tc.i8254.frequency: 0x00000000001234de
> kern.timecounter.tc.i8254.quality: 0000000000
>
> but now the mask is shown in hex (yay) but the others are shown
> in hex too (boo).
>
> The suggestion made (note that I'm carefully filing off names via
> passive voice :-) ) is that there could be a sysctl flag:
>
> #define CTLFLAG_DEFHEX 0x00000800
>
> that says that, without any additional formatting directive, the
> user-level "sysctl" command should output this particular value in
> hex. Obviously this eats up another flag bit (but there are a few
> left) and might require a new argument to the sysctl command
> ("force output to be decimal", for compatibility or whatever).
The format arg still exists. It used to be used to get unsigned and
hex formats, but is redundant for unsigned format and was rarely
used to specify hex format. Now it seems to only be used:
- for input, to distinguish between "IK" and other formats for
CTLTYPE_INT. ("IK" with other CTLTYPEs is only supported for
output)
- for output, to support 'K' and even more unparsable formats like
"S,clockinfo" and "S,vmtotal"
Getting hex format for a single special sysctl would have been almost
trivial when the X flag in the format was supported. Special cases
tend to need specially bloated dynamic attachment that needs 1 byte
to be changed to change the format string. For the example with
timecounters above:
X SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
X "mask", CTLFLAG_RD, &(tc->tc_counter_mask), 0,
X "mask for implemented bits");
SYSCTL_ADD_UINT() defaults a couple of parameters. Not enough to
make it less bloated, but enough to prevent you controlling its format
string.
X SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
X "counter", CTLTYPE_UINT | CTLFLAG_RD, tc, sizeof(*tc),
X sysctl_kern_timecounter_get, "IU", "current timecounter value");
Here it is trivial to change "IU" to "IX".
X SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
X "frequency", CTLTYPE_U64 | CTLFLAG_RD, tc, sizeof(*tc),
X sysctl_kern_timecounter_freq, "QU", "timecounter frequency");
This should use SYSCTL_ADD_UQUAD().
(The only differences are that it doesn't falsely claim to be MPSAFE,
and has a garbage size value.
Neither is MP safe on 32-bit arches, and the Giant locking given by
not claiming to be MPSAFE doesn't give any safeness for the 64-bit
variable accessed.
The garbage size value is apparently unused. The similar x86
machdep.tsc_freq sysctl has a garbage size value of 0, but this seems
to work too. In old versions, larger inconsistencies in the types
and sizes caused garbage reading the top 32 bits, but also made it
impossible to write these bits.
SYSCTL_*PROC() is harder to use than SYSCTL_*INTTYPE(), but using it
to specify a special ctltype or format is easy enough for a few uses.
Bruce
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