10-08-2002
I'll have to take your word for the list of entry points on SCO. It is a longer list than I used to seeing, but I haven't looked at many kernels.
You seem to asking how to verbally pronounce bdevsw and cdevsw. Gosh, I don't know. They're simply variable names. It never occurred to me to attempt to speak them nor have I ever heard anyone else try. It's obvious that the names come from "block device switch" and "character device switch". I hereby opine that the correct pronuciation is "bee dev switch" and "see dev switch" where "dev is pronounced like the first syllable of "devil". But I just made that up.
I am not really a Streams expert, but I *think* that your picture is wrong. First, I think that the modules on the read and write queues do indeed need to match. And in fact I think of it as a single module that simply handles both queues. I'd be a little surprised if I have this wrong.
Second, I am not sure if modules can peek at the queues of other modules or not. The case that has me worried is the need for exceptional processing for flow control. For example, in a tty driver driver, you may need to write an X-off character as soon as the read queues downstream start to back up. I am not at all sure about this, though.
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LEARN ABOUT OSF1
strmod_add
strmod_add(2) System Calls Manual strmod_add(2)
NAME
strmod_add - Adds STREAMS modules and drivers
SYNOPSIS
#include <sys/stream.h> dev_t strmod_add ( dev_t devno, struct streamtab *streamtab, struct streamadm *streamadm);
PARAMETERS
The device number (cdevsw slot) to use when adding a driver. If NODEV is supplied, the first available slot is used. This parameter is
ignored for modules. A pointer to the streamtab structure that contains the entry points. The actual streamtab structure has to be allo-
cated permanently in the driver's data space (as specified by System V Release 3.2). A pointer to the streamadm structure that contains
the administration parameters for the STREAMS module or driver. The actual streamadm structure is needed only for the duration of the
call. It does not have to be allocated permanently by the caller.
DESCRIPTION
The strmod_add() interface is used to configure STREAMS modules and drivers into the kernel. Specifically, it allows STREAMS drivers to
add entry points in character device switch tables. Modules are added to the STREAMS modules switch.
When adding a driver only, strmod_add() takes a device number, which is used to determine the device switch slot for the entry points. A
STREAMS driver can supply NODEV instead of a device number. In this case, strmod_add() finds the first available device switch slot and
returns the number actually used. If a device switch slot is already in use or if there are no slots available, NODEV is returned.
The streamtab parameter is a pointer to a traditional (System V Release 3.2) streamtab structure. The structure contains pointers to entry
points for the module's read and write queue routines.
The streamadm points to a streamadm structure. The streamadm structure provides additional information that is required under Tru64 UNIX.
NOTES
The device number can be constructed from the major number through the makedev macro, which is defined in /usr/include/sys/types.h.
RETURN VALUES
Upon successful completion, strmod_add() returns the device number associated with the device switch table. Otherwise, it returns NODEV.
RELATED INFORMATION
Data Structures: streamadm(4)
Routines: strmod_del(2) delim off
strmod_add(2)