(Sorry for the week delay; work has had me hosed into the ground.)

>Concerning the above problem (2 fds on the same 'sg' device) you could
>ban it with O_EXCL :-) 

This is exactly what I do... but it has to be O_EXCL and nonblocking, then change to 
blocking if it succeeds :-)

>Failing that I have implemented the 'pack-id'
>concept in the original 'struct sg_header' so you can fetch (read())
>using the pack_id given to the corresponding write(). For a SCSI
>read/write command the sector address would be a good candidate for
>the pack_id. Some co-operation between to the 2 apps holding those
>fds would be desirable. [If they were seperate apps they could use
>their pids as pack_ids].

There is still the potential for collision... and I don't like the
idea of applications requiring cooperative coding to function
together.  It's somewhat against UNIX design parameters.

How difficult is it to have the kernel keep the operations on a device
straight by fd?

>According to the MAINTAINERS file in 2.0.36 and 2.2.0-pre7 there is
>no current maintainer of 'sg'. Have I been looking in the wrong place?

I believe you're correct; there has been no real active maintainence
for a long time, just scattershot patches that don't have wide
distribution.  Until recently that is; it seems like development in
the generic packet area has suddently sprung to life again.
Seredipity and all that...

Monty

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