ccoohhttuunnee -- Command

Set a variable within a device driver
ccoohhttuunnee _d_r_i_v_e_r _t_a_g_f_i_e_l_d "_t_a_g_f_i_e_l_d = _v_a_l_u_e"

The  command ccoohhttuunnee  sets the  _t_a_g_f_i_e_l_d to _v_a_l_u_e  within the  given device
driver _d_r_i_v_e_r. You  can then use the command iiddmmkkccoohh  to build a new kernel
that incorporates your changes.  When you boot the new kernel, your changes
will have been made.

ccoohhttuunnee works by modifying the  file SSppaaccee.cc for _d_r_i_v_e_r. Each device driver
has  such a  file, that  sets user-definable  dimensions of  its operation.
When  you  invoke the  command  iiddmmkkccoohh  to build  a  new kernel,  COHERENT
automatically checks  whether a SSppaaccee.cc module  that have changed, compiles
it,  and links  it into  the newly built  kernel.  iiddmmkkccoohh  also recompiles
every SSppaaccee.cc whenever you change a tunable variable in the kernel, just to
ensure that all drivers are synchronized with changes in the kernel.

For  example,  the   file  /eettcc/ccoonnff/hhaaii/SSppaaccee.cc  gives  the  user-settable
variable for  the driver hhaaii, which  is COHERENT's host-adapter-independent
SCSI driver.  This file contains, among others, the variable HHAAII_TTAAPPEE. This
variable is a bit-map; bit _n is turned on if there is a SCSI tape device at
SCSI ID  _n. If you have  installed a SCSI tape as SCSI  device 3, then type
the following command:

    cohtune hai "HAI_TAPE" "int HAI_TAPE = 0x08"

The value 0x08  turns on bit 3.  As you  can see, ccoohhttuunnee finds the line in
/eettcc/ccoonnff/hhaaii/SSppaaccee.cc  that  contains   the  string  HHAAII_TTAAPPEE  and  is  not
commented out of the source, and replaces it with the line

    int HAI_TAPE = 0x08

You can read  a driver's SSppaaccee.cc to see how  you can configure it.  SSppaaccee.cc
also  gives some useful  clues as  to how  the driver works  and how  it is
currently configured.

You should _n_e_v_e_r modify a SSppaaccee.cc  by hand.  If you do so, you run the risk
of building a kernel that does not boot, or trashes your file system.

_S_e_e _A_l_s_o
ccoommmmaannddss, ddeevviiccee ddrriivveerrss, iiddeennaabbllee, iiddmmkkccoohh, iiddttuunnee

_N_o_t_e_s
ccoohhttuunnee cannot be used with STREAMS drivers.

Note that ccoohhttuunnee peforms no checks whatsoever on the content of the string
with which you  replace _t_a_g_f_i_e_l_d It should only be  used by people familiar
with C  programming, because setting  invalid values may  cause errors that
are difficult to diagnose.  _C_a_v_e_a_t _u_t_i_l_i_t_o_r.

Because of the primitive nature of ccoohhttuunnee, we recommend that users not use
it  directly, but  work  instead through  the  configuration shell  scripts
supplied  by the  driver's  developer (which  typically  live in  directory
/eettcc/ccoonnff/_d_r_i_v_e_r) that  can interactively generate the  correct sequence of
ccoohhttuunnee commands.
