[uml-user] Problem accessing /dev/raw devices inside of UML

[Doug D. <do...@ea...>]

I am having trouble trying to access "raw" partitions.  My setup is 
basically:

Kernel command line: umid=2000 con0=tty:/dev/pty/pty1000 
ubd0=sys/02000_cow,sys/8g_base ubd1=sys/02000_swap ubd2=/dev/raw/raw2 ...

The idea here is that /dev/ubd/2 points to /dev/raw/raw2 which is a 
"raw" mount of /dev/vg1/... (a Linux Volume Manager) mount.

The mount works and the file can be opened, but it canned be accessed. 
I did an strace of linux and a 1024 byte read operation inside of the UM 
becomes

open("/dev/raw/raw2", O_RDWR|O_LARGEFILE) = 22
read(22, 0xa7836000, 4120)              = -1 EINVAL (Invalid argument)

I know that raw partitions have read restrictions on alignment and 
operand size.  It apears that UML is trying to read 4120 bytes when I 
only asked for 1024 in my test program.  In that 4120 is not a multiple 
of 512, it would be expected that this fails.  Anyone have any idea 
where the UML kernel is getting 4120 from?

-- 
Doug Dumitru
EasyCo LLC
949 831-4774