>> Why should the character interface be connected to the block layer?
>> This would contradict UNIX rules.
>How would it? At some layer, the two are merged anyway (for example, at least
>on disk you'll have blocks again). Doing it up high means more unified code
>below.
Just a hint: the block layer is for caching blocks from disk type deveices.
- Block device access is always going directly into the block cache.
So the I/O is always kernel I/O. In addition, it is async I/O - the
block layer fires it up and may wait for it later after sending out other
requests.
- Character device access is synchronous access and may be either kernel
or user space DMA access. In most cases, it is user space DMA access.
How try to ask your question again...
>> AFAIK, tagged command queuing is a SCSI specific property, why should this
>> be part of a generif block layer?
>That is not true. Late IDE also has this, and systems like drbd - which
>currently uses a quite clever heuristic to deduce barriers - could also
>utilize this input.
How is it implemented?
Jörg
EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
js@cs.tu-berlin.de (uni) If you don't have iso-8859-1
schilling@fokus.gmd.de (work) chars I am J"org Schilling
URL: http://www.fokus.gmd.de/usr/schilling ftp://ftp.fokus.gmd.de/pub/unix
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