PR1245 device lseek
strauman at slac.stanford.edu
Tue Aug 7 22:53:32 CDT 2007
Victor Vengerov wrote:
> Hard disk etc. represented in RTEMS device driver with
> open/close/read/write/control interface. rtems_libio_rw_args_t argument
> is passed to device read/write primitives, which contains the offset
> attribute. offset filled in device_write (deviceio.c) from iop->offset.
> May be I've missed something, but it looks for me you just need to
> adjust iop->offset
That's already done in libcsupport/src/lseek.c.
However, the iop->offset adjustment is undone if
I can see two valid scenarios:
a) a device for which adjusting iop->offset is all that's needed.
In this case, the lseek_h() method (in the case discussed here
this is 'device_lseek()') should return the current offset (not 0).
b) non-seekable device should return -1 (not 0) and set errno
If we assume that currently only a) is implemented [and we don't want
to break existing code that assumes these semantics] then
either device_lseek() should return the current offset or
lseek.c should be fixed to return the current offset if lseek_h
> in device_lseek in accordance to offset and whence
> Joel Sherrill wrote:
>> This PR notes that device_lseek() always succeeds but
>> does nothing. According to OpenGroup
>> lseek() should return ESPIPE for ttys, sockets, and pipes.
>> I may be having a brain freeze, but right now, I don't
>> see how to implement a seek on a block device like
>> a hard disk. I know you have to be able to do it.
>> Any thoughts?
>> rtems-users mailing list
>> rtems-users at rtems.com
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