On 30/09/17 14:08, Holger Hoffstätte wrote:
> A "root" subvolume is identified by a null parent UUID, so adding a new
> subvolume filter and flag -P ("Parent") does the trick.
I don't like the naming. The flag you are proposing is really nothing to
do with whether a subvolume is a parent or not: it is about whether it
is a snapshot or not (many subvolumes are both snapshots and also
parents of other snapshots, and many non-snapshots are not the parent of
any subvolumes).
I have two suggestions:
1) Use -S (meaning "not a snapshot", the inverse of -s). Along with this
change. I would change the usage text to say something like:
-s list subvolumes originally created as snapshots
-S list subvolumes originally created not as snapshots
Presumably specifying both -s and -S should be an error.
2) Add a -P (parent) option but make it take an argument: the UUID of
the parent to match. This would display only subvolumes originally
created as snapshots of the specified subvolume (which may or may not
still exist, of course). A null value ('' -- or a special text like
'NULL' or 'NONE' if you prefer) would create the search you were looking
for: subvolumes with a null Parent UUID.
The second option is more code, of course, but I see being able to list
all the snapshots of a particular subvolume as quite useful.
If you do choose the second option you need to decide what to do if the
-P is specified more than once. Probably treat it as an error (unless
you want to allow a list of UUIDs any of which can match). You might
also want to reject an attempt to specify both -s and -P.
Graham
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