Re: OT: Windows (Was: Re: Open Source does not mean easily

On Tue, 07 Jan 2025 19:09:53 GMT
scott@slp53.sl.home (Scott Lurndal) wibbled:

cross@spitfire.i.gajendra.net (Dan Cross) writes:

In article <vGbfP.54357$XfF8.7280@fx04.iad>,
Scott Lurndal <slp53@pacbell.net> wrote:

cross@spitfire.i.gajendra.net (Dan Cross) writes:

In article <vlioum$24bqm$1@dont-email.me>,  <Muttley@DastardlyHQ.org> wrote:

>
>

Applications in those days (e.g. fsck) would access the
raw character device using the unbuffered read() and
write() system calls rather than using stdio.  A key
characteristic of raw devices were that the hardware DMA would
use the application buffer directly rather than copying
the data to the kernel buffer pool first.

>
They still do!

>
Well, not on linux.  Even O_DIRECT still goes through
the file cache, last I checked.
>
I submitted a 'raw device' patch to the linux mailing
list in the late 90s while at SGI.   It wasn't accepted because
O_DIRECT was considered sufficient, even with the spurious
copy.  The overhead of pinning the user space pages was
considered onerous.

I vaguely remember Oracle complaining about this back in the day meaning
they couldn't guarantee their RDBMS transaction writes on Linux. Not sure
if or when it was solved.