Messages in this thread | | | Date | Wed, 17 Sep 2014 12:59:30 -0400 | From | Theodore Ts'o <> | Subject | Re: [PATCH 2/7] Define new syscalls readv2,preadv2,writev2,pwritev2 |
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On Wed, Sep 17, 2014 at 12:05:23PM -0400, Milosz Tanski wrote: > Theodore, > > I might be missing understanding something, but... I already omitted > read2 and write2 which can be implemented in userspace by libc (as you > pointed out). In the case of readv vs. preadv there's an extra > positional argument (file offset) and preadv version doesn't change > the file location. I didn't want to overload the meaning of preadv2 to > take a special negative offset value that uses the current file > position but also changes the file position.
off_t has to be signed, so having a magic negative value doesn't bother me that much. Or you could use a flag bitvalue which means to use the fd's offset and to ignore the positional value. (More bike-shedding :-)
The main reason why I mention it is we have a huge number of read/write syscalls already, and if we add yet another to support scatter-gather lists on the memory side, we'll be adding another factor of two more read/write system calls. So the suggestion was one of trying to (probably fruitlessly) trying to stem the expnoential increase in read/write system calls. :-)
Cheers,
- Ted
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