On Tuesday August 7, [EMAIL PROTECTED] wrote:
> On 8/7/07, Neil Brown <[EMAIL PROTECTED]> wrote:
> > On Monday August 6, [EMAIL PROTECTED] wrote:
> > > On Tue, 2007-08-07 at 16:07 +1000, Neil Brown wrote:
> > > > Suppose that in a program I have an open file descriptor for a device,
> > > > and I want to find the /sys/block information for this device.
> > > > There is currently no direct way to do this. I need to read
> > > > /sys/block/*/dev, /sys/block/*/*/dev
> > > > and match major/minor numbers with the result from fstat.
> > > >
> > > > I would like a more direct mechanism.
>
> $ udevinfo --query=path --name=sda
> /block/sda
If I interpret the result of 'strace' properly, this looks at
/dev/.udev/names/sda
and prints the result after decoding '\x2f' as '/'.
I want to go from an open file descriptor, or at least an entry in
/dev.
And I don't think I want to depend on udev if I can avoid it....
> >
> > That makes a lot of sense.
> > So it would return "block/sda/sda1" now,
>
> Every devpath always starts with a '/' in the kernel, its kind of
> weird, but we should not introduce a new variation of it. :)
Fair comment. So
/block/sda/sda1
now, and whatever later.
>
> They can be definitely longer than than 256, probably not longer than
> 512 today, but you can't be sure about that.
I guess we go for PATH_MAX then?
Any idea how to get a sysfs path in a generic way?
I tried:
struct inode *inode = filp->f_path.dentry->d_inode;
struct kobject *ko = NULL;
char *path = NULL;
if (S_ISBLK(inode->i_mode) &&
inode->i_bdev &&
inode->i_bdev->bd_disk)
ko = &inode->i_bdev->bd_disk->kobj;
if (S_ISCHR(inode->i_mode) &&
inode->i_cdev)
ko = &inode->i_cdev->kobj;
if (ko)
path = kobject_get_path(ko, GFP_KERNEL);
For /dev/sda, it returns /block/sda which is good.
For /dev/sda1 it still returns /block/sda which is not good.
For /dev/null it returns /mem which doesn't even exist in sysfs
For /dev/tty it doesn't return anything.
I'm tempted to just implement it for block devices and let someone
else worry about char devices.
Thanks,
NeilBrown
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