On Wed, 21 Feb 2007, Brian Utterback wrote:
> Because of the design of streams, it is sometimes the case that one
> would like to increase the stream head queue size. Streams modules
> can do this, but there is no way to do it outside the stream, except
> by increasing the default value.
>
> The defaults are controlled by a struct called "strm_info". If I print
> this out I get:
>
>> strm_info::print
> {
> mi_idnum = 0
> mi_idname = 0x18640f0 "strrhead"
> mi_minpsz = 0
> mi_maxpsz = 0xffffffffffffffff
> mi_hiwat = 0x1400
> mi_lowat = 0x400
> }
>>
>
> The time honored incantation that services uses to set this for
> customers is:
>
> echo strm_info+0x2c/W 3e030 | /usr/bin/mdb -kw /dev/ksyms
>
> This bothers me for several reasons. First, the use of the constant
> offset 0x2c. Second, that the location specified by strm_info+0x2c
> is the lower half of the mi_lowat member, which I think will be
> a problem on x86.
>
> However, I can't seem to find a way to specify symbolically the
> mi_lowat location for writing. It didn't work to specify
> strm_info.mi_lowat as the address. Is there something I'm missing?
Well, using:
> strm_info::print -a mi_lowat
fffffffffbc76360 mi_lowat = 0x400
you get the address. It is possible to shellscript this into an
automatism; but I don't know if it's possible with one mdb pipe.
Extracting just the address from above works via e.g.:
> ::eval 'strm_info::print -a mi_lowat ! cut -d" " -f1'
fffffffffbc76360
but mdb doesn't accept a pipe '|' after ::eval anymore, I.e. what would've
been obvious for me to try:
> ::eval 'strm_info::print -a mi_lowat ! cut -d" " -f1' | /W 3e030
doesn't work, anything after the last '|' on this line is just ignored.
I'd be extremely grateful for an ability to get the output of:
::offsetof
::sizeof
::eval
into an mdb variable; Can this be done somehow ?
FrankH.
