On Apr 29, 2006, at 03:53:11, Greg KH wrote:
The update process is triggered when writing 'something' into the
'update' file at the top level hypfs directory. You can do this
e.g. with 'echo 1 > update'. During the update the whole directory
structure is deleted and built up again.
This sounds a lot like configfs. Why not use that instead?
Is there a reason that sysfs can't be used for a lot of these
things too?
We already have the different cpus in sysfs, why put things in a
different location than that?
It sounds like a lot of things need some kind of shell-scriptable
transaction interface for sysfs files. You don't want to have more
than one value per file, but reading or writing of some values must
be done together for consistency reasons. Is there any way to
implement something like this? This would work for the framebuffer
people and solve the needs of a lot of the people who still want
ioctls or some other atomic-multivalued transfer that would otherwise
be a great sysfs candidate.
# Start a transaction
exec 3</sys/hypervisor/s390/transaction
# Add another reference to the transaction
exec 4<&3
# List CPUs and info
cd /sys/hypervisor/s390/cpus
for i in *; do
echo "CPU $i: type=`cat type` mgmtime=`cat mgmtime`"
done
# Transaction does *not* end here
exec 3<&-
# List CPUs again a different way
ls /sys/hypervisor/s390/cpus
# Transaction does end here
exec 4<&-
A process that doesn't care about the transaction (Like a user
inspecting from a shell), could just cd in and cat random files, and
it would run a transaction for each file opened, and end the
transaction when the file is closed. Obviously that's inefficient,
but it's obviously correct and works. Otherwise, from opening the
transaction filehandle for the first time till closing the last open
FD to it, the process would get a consistent view of the data, read
when the "transaction" file is first opened opened. Perhaps any
modifications would be synced and written at the close of that
filehandle.
I don't know if that's something doable given the FD model, but if it
is, then that's trivial to use for the admin, in shell scripts, perl
scripts, C programs, etc. It also works with the one-value-per-file
sysfs model.
Cheers,
Kyle Moffett
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