Date: Wed, 17 May 2000 13:46:55 -0400 From: Joy Ganguly <joy@niksun.com> To: Alfred Perlstein <bright@wintelcom.net>, freebsd-hackers <freebsd-hackers@freeBSD.org> Subject: Re: Question about file write???? Message-ID: <3922DB0F.9D9095C9@falcon.niksun.com> References: <20000517160746.12768.qmail@www0a.netaddress.usa.net> <20000517102516.B14968@fw.wintelcom.net>
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Alfred Perlstein wrote:
> * Joy Ganguly <joy.ganguly@usa.net> [000517 09:41] wrote:
> >
> > hi all,
> >
> > i have written a special ioctl which writes data into a file from a buffer in
> > kernel memory. it invokes fo->fo_write() and involves one copy from kernel
> > mem
> > to disk cache. however this takes substantially more time than an ordinary
> > write which copies from user space to the disk cache. any explanations???
>
> What are you using for your kernel to kernel copy?
>
fo->fo_write uses uiomove() with seg_flg = UIO_SYSSPACE. uiomove() uses
bcopy() to do the actual copying. my ioctl sets up the struct uio to point to the
kernel buf and calls fo->fo_write(). Hence the only difference between my ioctl
and original write is that the former has seg_flg = UIO_SYSSPACE and the latter
has UIO_USERSPACE.
>
> (copyin and friends are hand optimized for great speed when copying
> from/to userspace)
>
what sort of optimizations are you referrring to?? is there some other way i can
do this??
>
> --
> -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
> "I have the heart of a child; I keep it in a jar on my desk."
>
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