davec@hammer.UUCP (03/22/84)
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I am in the process of implementing a couple of device
drivers to run with a 4.2 BSD kernel. The devices use DMA,
so I am planning not to implement the scatter/gather I/O
functionality of the "readv" and "writev" system calls
for these drivers.
Can anyone tell me if this will break Unix? I cannot
find any examples of utilities or systems that use
readv/writev now, so do not believe that it should
make much difference.
Dave Cobbley
Tektronix, Inc.
Wilsonville, Oregon
{decvax, ucbvax}!tektronix!tekecs!davecwls@astrovax.UUCP (William L. Sebok) (03/23/84)
> I am in the process of implementing a couple of device > drivers to run with a 4.2 BSD kernel. The devices use DMA, > so I am planning not to implement the scatter/gather I/O > functionality of the "readv" and "writev" system calls > for these drivers. > Can anyone tell me if this will break Unix? I cannot > find any examples of utilities or systems that use > readv/writev now, so do not believe that it should > make much difference. > Dave Cobbley Tektronix, Inc. I myself have been writing a driver for an image display card from Peritec Inc. Implementing the scatter/gather code complicates things quite a bit. I would also like to know when this need for this to be implemented in one system call (above and beyond using a series of read/write calls), is great enough to justify the extra trouble in the kernel (where after all there is supposed to be some attempt to keep things "simple"). All of the dma drivers in the distribution implement the scatter/gather stuff in the higher level routines that are used by/call the driver. For instance the scatter/gather for the raw unbuffered devices is implemented in physio(). -- Bill Sebok Princeton University, Astrophysics {allegra,akgua,burl,cbosgd,decvax,ihnp4,kpno,princeton,vax135}!astrovax!wls