bruce@bmhalh.UUCP (Bruce M. Himebaugh) (08/19/90)
I am writing a character device driver under SCO Xenix (v2.3.3) and have run
across a stumbling block. During the read and write functions I wish to
access the current file postition (as set by lseek(S)). Per the documentation
that I have I access the element u_offset in the 'u' structure. This works
great for 0-65535. But, when I tell lseek(S) to move to postition 65536 the
value of u_offset gets set to 0 and if I move to 65537 it gets set to 1, etc.
I have the feeling that u_offset is just a an offset into the current segment
and when accessing values outside 65535 I am actually moving the file pointer
into another segment, but how do I tell what that segment is? Hopefully I am
partially on the right track, but if I'm not I would appreciate some direction.
I have programmed in C for quite a while, but am just now tackling device
drivers.
A second question is, where can I get a book (or books) on writing XENIX device
drivers? I have a book on UNIX device drivers, but Xenix is enough different
that it doesn't answer all my questions.
Any help on these two questions will be GREATLY appreciated.
Thanks,
Bruce
--
Bruce M. Himebaugh Voice: 216-484-3528
PATHS: uunet!{ncoast,aablue}!fmsystm!bmhalh!bruce
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*NOTE*: Please do not use bruce@bmhalh.UUCP -- I'm not registered yet.cpcahil@virtech.uucp (Conor P. Cahill) (08/29/90)
First off, don't do this: >Followup-To: poster It gets people mad when they do a follow-up to somebody named poster on the local machine. If you want help, just leave the follow-up off. In article <24@bmhalh.UUCP> bruce@bmhalh.UUCP (Bruce M. Himebaugh) writes: >I am writing a character device driver under SCO Xenix (v2.3.3) and have run >across a stumbling block. During the read and write functions I wish to >access the current file postition (as set by lseek(S)). Per the documentation >that I have I access the element u_offset in the 'u' structure. This works >great for 0-65535. But, when I tell lseek(S) to move to postition 65536 the >value of u_offset gets set to 0 and if I move to 65537 it gets set to 1, etc. This sounds like you are using the u_offset as a short (or int) when it is really a long. The type of u_offset is usually a typedef (off_t) in /usr/include/sys/types.h. > >A second question is, where can I get a book (or books) on writing XENIX device >drivers? I have a book on UNIX device drivers, but Xenix is enough different >that it doesn't answer all my questions. Writing a Unix Device Driver by Janet Egan and Thomas Teixeira Published by John Wiley & sons. -- Conor P. Cahill (703)430-9247 Virtual Technologies, Inc., uunet!virtech!cpcahil 46030 Manekin Plaza, Suite 160 Sterling, VA 22170