On 2018-05-17 10:46, Jeff Mahoney wrote:
On 5/16/18 6:35 PM, David Sterba wrote:
On Wed, May 16, 2018 at 06:03:56PM +0800, Anand Jain wrote:
Not yet ready for the integration. As I need to introduce
-o no_read_mirror_policy instead of -o read_mirror_policy=-<devid>
Mount option is mostly likely not the right interface for setting such
options, as usual.
I've seen a few alternate suggestions in the thread. I suppose the real
question is: what and where is the intended persistence for this choice?
A mount option gets it via fstab. How would a user be expected to set
it consistently via ioctl on each mount? Properties could work, but
there's more discussion needed there. Personally, I like the property
idea since it could conceivably be used on a per-file basis.
For the specific proposed use case (the tests), it probably doesn't need
to be persistent beyond mount options.
However, this also allows for a trivial configuration using a slow
storage device to provide redundancy for a fast storage device of the
same size, which is potentially very useful for some people. In that
case, I can see most people who would be using it wanting it to follow
the filesystem regardless of what context it's being mounted in (for
example, it shouldn't need an extra option if mounted from a recovery
environment or if it's moved to another system).
Most of my reason for recommending properties is that filesystem level
properties appear to be the best thing BTRFS has to store per-volume
configuration that's supposed to stay with the volume, despite not
really being used for that even though there are quite a few mount
options that are logical candidates for this type of thing (for example,
the `ssd` options, `metadata_ratio`, and `max_inline` all make more
logical sense as a property of the volume, not the mount).
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