Re: [PATCH] [ConfigFS]: Allow symbolic links from a SysFS structkobject source.
From: Nicholas A. Bellinger
Date: Fri Oct 17 2008 - 16:07:56 EST
On Fri, 2008-10-17 at 12:48 -0700, Joel Becker wrote:
> On Fri, Oct 17, 2008 at 01:22:18AM -0700, Nicholas A. Bellinger wrote:
> > On Fri, 2008-10-17 at 00:44 -0700, Greg KH wrote:
> > > What is the problem you are attempting to solve here?
> > >
> > So, the generic target_core_mod engine that lives
> > under /sys/kernel/config/target/core needs a method to locate struct
> > block_device and struct scsi_device for access via bio_submit() and
> > scsi_execute_() respectively.
> > Originally, target_core_mod used key echoed through configfs attributes
> > like so:
> > export TARGET=/sys/kernel/config/target/core/
> > # Create $STORAGE_OBJECT of type Linux/BLOCK in generic target_core_mod
> > mkdir -p $TARGET/iblock_0/lvm_test0
> > # OLD METHOD to reference struct block_device
> > echo iblock_major=254,iblock_minor=2 > $TARGET/iblock_0/lvm_test0/control
> > echo 1 > $TARGET/iblock_0/lvm_test0/enable
> > # NEW METHOD using sysfs ->configfs symlinks to reference struct block_device
> > ln -s /sys/block/dm-2 $TARGET/iblock_0/lvm_test0/dm-2
> Pass an open file descriptor. In bash(1):
> exec 3<>/dev/dm-7
> echo 3 >$TARGET/iblock_0/lvm_test0/control # I'd call it 'fd'
> In kernel, in the ->store() function of 'control':
> p = (char *)page;
> fd = simple_strtol(p, &p, 0);
> filp = fget(fd);
> inode = igrab(filp->f_mapping->host);
> dev = I_BDEV(filp->f_mapping->host);
> blkdev_get(dev, FMODE_WRITE | FMODE_READ, 0);
> Error handling is left up to you (validate the strtol, fd range, ISBLK,
> etc). This assumes you want the struct block_device and want to pin it
> in memory. I assume you do.
Btw, ideally I would like to do the same type of thing for accessing
drivers/scsi for both TYPE_DISK and non TYPE_DISK.. I will have a look
and see if something is possible to access struct scsi_device in all
device type cases..
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