Messages in this thread | | | Date | Mon, 18 Oct 1999 14:01:46 +0100 (MET) | From | DAVID BALAZIC <> | Subject | Confused about RAW devices ... |
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Supposedly raw devices are going into kernel 2.4 ( http://linuxtoday.com/story.php3?sn=10698 )
I'm confused a bit ? What are those raw devices ?
The mentioned article says : > A raw device is one whose accesses are not handled through the caching > layer and whose actions are immediately and always synchronous with the > "hard" data on the disk or elsewhere.
How is this different from normal devices ?
I did a small test : (2) fd=open("/dev/cdrom",O_RDONLY); read(fd,buffer,1); wait_a_second(); read(fd,buffer,1);
When the second read is done , the CD-drive spins the CD up and the drive LED blinks. No sign of caching. ( kernel v2.2.12 )
And even if there were, using the O_SYNC flag should tell the driver : "Don't cache this , dude !" and there is no need for new device files.
A related question : Why are accesses to devices ( /dev/cdrom and /dev/fd0 are the ones I tested ) NOT cached ?
Am I missing something important ?
-- David Balazic , student E-mail : 1stein@writeme.com | living in sLOVEnija home page: http://surf.to/stein Computer: Amiga 1200 + Quantum LPS-340AT --
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