On 07.05.20 13:43, Miklos Szeredi wrote: > On Thu, May 7, 2020 at 12:56 PM Max Reitz <[email protected]> wrote: >> >> On 06.05.20 18:04, Dr. David Alan Gilbert wrote: >>> * Max Reitz ([email protected]) wrote: >>>> Whenever we encounter a directory with an st_dev that differs from that >>>> of its parent, we set st_rdev accordingly so the guest can create a >>>> submount for it. >>>> >>>> Make this behavior optional, so submounts are only announced to the >>>> guest with the announce_submounts option. Some users may prefer the >>>> current behavior, so that the guest learns nothing about the host mount >>>> structure. >>>> >>>> Signed-off-by: Max Reitz <[email protected]> >>> >>> Does this need to be wired to a flag in the INIT message (like say >>> FUSE_ASYNC_READ) to indicate that the kernel/daemon supports this, or is >>> it really safe just to start sending the changed rdev? >> >> I supposed it to be safe, given that rdev is never used for anything but >> device files, so basically it was just a reserved field for directories. > > You assume only directories can be mounted, but that's not so. A > device can also be the source or destination of a bind mount.
Well, I mostly thought this case wouldn’t be too important. But I suppose it doesn’t make sense to decide now that it’s never going to be important. > We need to extend fuse_entry_out with a flags field. We could > possibly reuse the upper bits of entry_valid (i.e. timeouts above say > INT_MAX seconds could be taken as "infinity"). Unfortunately that's > not as easy as splitting it into two fields due to endianness :( For the time being, a single bit would be sufficient to signify whether there should be a submount at all. We could add a field with a submount ID (i.e., st_dev from the host) in the future when we decide we want/need to ensure that two inodes with the same st_dev on the host also have the same st_dev in the guest. Max
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