On Thu, Mar 8, 2018 at 8:51 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > On Thu, Mar 8, 2018 at 4:38 AM, yangerkun <yangerkun@xxxxxxxxxx> wrote: >> > [...] >>>>> >>>>> In fsck.overlay, lower layer file/dir may be modified with there is not >>>>> I_OVL_INUSE in lower layer, but we cannot check does lower layer mounted >>>>> with I_OVL_INUSE. >>>>> >>>> > [...] >>> Also, if we follow my suggestion above for upperdir/workdir >>> fsck.overlay may still >>> try to aquire I_OVL_INUSE on lowerdir with O_EXCL|O_DIRECTORY and kernel >>> can test I_OVL_INUSE flag on lowerdir without trying to set it on mount. >> >> >> It's good when we want to mount overlayfs with fsck.overlay is running; But >> when there is a mounted overlayfs before fsck.overlay, we cannot use this >> way to check if the lower layer has already been used. > > Perhaps we should acquire a shared POSIX lock from kernel on lower/upper/work > dirs and fsck.overlay should acquire an exclusive POSIX lock. > > I'm not sure how acquiring a POSIX lock from kernel should work and which > task should be the owner of the lock, but generally overlayfs could either have > a single owner task in the kernel for all super blocks or one owner > per sb, in which > case, we could acquire an exclusive lock on work/upper dirs instead of using > the custom I_OVL_INUSE lock. > > Just a thought - not sure if this makes sense. CC'ing Jeff for reality check. Much better to use flock(2) locks which, unlike POSIX locks, have sane semantics. The owner is not a task but a file, so just need to keep an file open referring to each layer's root in overlayfs. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
