livecd July 2015

livecd@lists.fedoraproject.org

2 participants
2 discussions

Re: [Fedora-livecd-list] [dm-devel] Unnecessary snapshot validation
by Frederick Grose 30 Jul '15

30 Jul '15

On Sun, Jun 21, 2015 at 4:31 PM, Mikulas Patocka <mpatocka(a)redhat.com> wrote: > > > On Fri, 30 Jan 2015, Alasdair G Kergon wrote: > >> I've had a complaint tonight at FOSDEM that we invalidate old-style >> snapshots in a particular case where there is no need to! >> >> If you take a snapshot of an origin, then keep writing to the *snapshot* >> and fill it up we should just return errors on any further such writes >> *without* invalidating the snapshot - so reads can still be performed >> successfully. >> >> (check for -ENOSPC from prepare_exception in __find_pending_exception?) >> >> Alasdair > > Hi > > Here I'm sending a patch that keeps data when the snapshot fills up. > > The user can extend the overflowed snapshot, deactivate and activate it > again, run fsck (if journaling filesystem is not used) mount it and > recover the data. > > Mikulas > > > > From: Mikulas Patocka <mpatocka(a)redhat.com> > > dm snapshot: don't invalidate on-disk image on snapshot write overflow > > When the snapshot overflows because of a write to the origin, the on-disk > image has to be invalidated. However, when the snapshot overflows because > of a write to the snapshot, the on-disk image doesn't have to be > invalidated. This patch changes the behavior, so that the on-disk image is > not invalidated in this case. > > When the snapshot overflows, the variable snapshot_overflowed is set. All > writes to the snapshot are disallowed to minimize filesystem corruption - > this condition is cleared when the snapshot is deactivated and activated. > > Signed-off-by: Mikulas Patocka <mpatocka(a)redhat.com> > > --- > drivers/md/dm-snap.c | 18 ++++++++++++++---- > 1 file changed, 14 insertions(+), 4 deletions(-) > > Index: linux-4.1-rc8/drivers/md/dm-snap.c > =================================================================== > --- linux-4.1-rc8.orig/drivers/md/dm-snap.c 2015-06-19 20:57:04.000000000 +0200 > +++ linux-4.1-rc8/drivers/md/dm-snap.c 2015-06-21 17:11:10.000000000 +0200 > @@ -63,6 +63,13 @@ struct dm_snapshot { > */ > int valid; > > + /* > + * The snasphot overflowed because of write to the snapshot device. > + * We don't have to invalidate the snapshot in this case, but we need > + * to prevent further writes. > + */ > + int snapshot_overflowed; > + > /* Origin writes don't trigger exceptions until this is set */ > int active; > > @@ -1152,6 +1159,7 @@ static int snapshot_ctr(struct dm_target > > s->ti = ti; > s->valid = 1; > + s->snapshot_overflowed = 0; > s->active = 0; > atomic_set(&s->pending_exceptions_count, 0); > s->exception_start_sequence = 0; > @@ -1301,6 +1309,7 @@ static void __handover_exceptions(struct > > snap_dest->ti->max_io_len = snap_dest->store->chunk_size; > snap_dest->valid = snap_src->valid; > + snap_dest->snapshot_overflowed = snap_src->snapshot_overflowed; > > /* > * Set source invalid to ensure it receives no further I/O. > @@ -1692,7 +1701,7 @@ static int snapshot_map(struct dm_target > * to copy an exception */ > down_write(&s->lock); > > - if (!s->valid) { > + if (!s->valid || (unlikely(s->snapshot_overflowed) && bio_rw(bio) == WRITE)) { > r = -EIO; > goto out_unlock; > } > @@ -1716,7 +1725,7 @@ static int snapshot_map(struct dm_target > pe = alloc_pending_exception(s); > down_write(&s->lock); > > - if (!s->valid) { > + if (!s->valid || s->snapshot_overflowed) { > free_pending_exception(pe); > r = -EIO; > goto out_unlock; > @@ -1731,7 +1740,8 @@ static int snapshot_map(struct dm_target > > pe = __find_pending_exception(s, pe, chunk); > if (!pe) { > - __invalidate_snapshot(s, -ENOMEM); > + s->snapshot_overflowed = 1; > + DMERR("Invalidating snapshot: Unable to allocate exception."); > r = -EIO; > goto out_unlock; > } > @@ -1987,7 +1997,7 @@ static void snapshot_status(struct dm_ta > > down_write(&snap->lock); > > - if (!snap->valid) > + if (!snap->valid || snap->snapshot_overflowed) > DMEMIT("Invalid"); > else if (snap->merge_failed) > DMEMIT("Merge failed"); > > -- > dm-devel mailing list > dm-devel(a)redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel If I read this correctly, this change will allow Live USB devices (having read-only origins) to overflow their overlay file and not crash with I/O errors and fail to boot because of the invalid overlay. Is this correct? If so, when would this released, and could it be back ported to F21 & F22 updates? --Fred

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Update to liveimage-mount
by Frederick Grose 20 Jul '15

20 Jul '15

I've submitted a pull request, https://github.com/rhinstaller/livecd-tools/pull/9 for an update to liveimage-mount. There are many integrated updates -- best reviewed by test driving. Include a datetime tag to easily distinguish in-the-wild versions. Provide infile utility and error-handling functions to permit standalone usage. Provide option to skip error raising on subprocess calls. Add support for live mounting a directory of LiveOS contents. Add a /run/initramfs/livedev link and a /run/initramfs/live bind mount to simulate the LiveOS booted environment. Add an option to mount filesystems read-only; and report the persistence status upon entering the command shell. Create a non-existent mount directory, if needed, and remove it on exit. Add support for DNF and/or Yum repository caches. Use the /run tmpfs instead of /dev/shm. Create non-persistent metadata type snapshot targets for in-memory overlays. Use random device mapper & mount point names on successive invocations. Support encrypted home filesystems. Call programs by basename only, relying on $PATH searching. Cleanup white space and line lengths.

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livecd July 2015