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Currently user space utilizes dev info ioctl to grab the info of a
certain devid, this includes its device uuid. But the returned info is
not enough to determine if a device is a seed.
Commit a26d60dedf ("btrfs: sysfs: add devinfo/fsid to retrieve actual
fsid from the device") exports the same value in sysfs so this is for
parity with ioctl. Add a new member, fsid, into
btrfs_ioctl_dev_info_args, and populate the member with fsid value.
This should not cause any compatibility problem, following the
combinations:
- Old user space, old kernel
- Old user space, new kernel
User space tool won't even check the new member.
- New user space, old kernel
The kernel won't touch the new member, and user space tool should
zero out its argument, thus the new member is all zero.
User space tool can then know the kernel doesn't support this fsid
reporting, and falls back to whatever they can.
- New user space, new kernel
Go as planned.
Would find the fsid member is no longer zero, and trust its value.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.