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SubjectRe: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17]
On Mon, Feb 24, 2020 at 3:55 PM James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:

> Once it's table driven, certainly a sysfs directory becomes possible.
> The problem with ST_DEV is filesystems like btrfs and xfs that may have
> multiple devices.

For XFS there's always a single sb->s_dev though, that's what st_dev
will be set to on all files.

Btrfs subvolume is sort of a lightweight superblock, so basically all
such st_dev's are aliases of the same master superblock. So lookup of
all subvolume st_dev's could result in referencing the same underlying
struct super_block (just like /proc/$PID will reference the same
underlying task group regardless of which of the task group member's
PID is used).

Having this info in sysfs would spare us a number of issues that a set
of new syscalls would bring. The question is, would that be enough,
or is there a reason that sysfs can't be used to present the various
filesystem related information that fsinfo is supposed to present?

Thanks,
Miklos

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