MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

MFC r256571:
Add a function, memstr, which can be used to convert a buffer of
null-separated strings to a single string. This can be used to print the
full arguments of a process using execsnoop (from the DTrace toolkit) or
with the following one-liner:

dtrace -n 'syscall::execve:return {trace(curpsinfo->pr_psargs);}'

Note that this relies on the process arguments being cached via the struct
proc, which means that it will not work for argvs longer than
kern.ps_arg_cache_limit. However, the following rather non-portable
script can be used to extract any argv at exec time:

fbt::kern_execve:entry
{
printf("%s", memstr(args[1]->begin_argv, ' ',
args[1]->begin_envv - args[1]->begin_argv));
}

The debug.dtrace.memstr_max sysctl limits the maximum argument size to
memstr().

MFC r262665:
Expose a few DTrace parameters as sysctls under kern.dtrace and add
descriptions for several existing sysctls.

PR: 187027

MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

MFC r256571:
Add a function, memstr, which can be used to convert a buffer of
null-separated strings to a single string. This can be used to print the
full arguments of a process using execsnoop (from the DTrace toolkit) or
with the following one-liner:

dtrace -n 'syscall::execve:return {trace(curpsinfo->pr_psargs);}'

Note that this relies on the process arguments being cached via the struct
proc, which means that it will not work for argvs longer than
kern.ps_arg_cache_limit. However, the following rather non-portable
script can be used to extract any argv at exec time:

fbt::kern_execve:entry
{
printf("%s", memstr(args[1]->begin_argv, ' ',
args[1]->begin_envv - args[1]->begin_argv));
}

The debug.dtrace.memstr_max sysctl limits the maximum argument size to
memstr().

MFC r262665:
Expose a few DTrace parameters as sysctls under kern.dtrace and add
descriptions for several existing sysctls.

PR: 187027