| Message ID | 20191118133816.3963-1-idryomov@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | wip-krbd-readonly | expand |
Hi Ilya, On 11/18/2019 09:38 PM, Ilya Dryomov wrote: > Hello, > > This series makes read-only mappings compatible with read-only caps: > we no longer establish a watch, Although this is true in userspace librbd, I think that's wired: when there is someone is reading this image, it can be removed. And the reader will get all zero for later reads. What about register a watcher but always ack for notifications? Then we can prevent removing from image being reading. Ilya, Jason, what's your opinion? Thanx > acquire header and object map locks, > etc. In addition, because images mapped read-only can no longer be > flipped to read-write, we allow read-only mappings with unsupported > features, as long as the image is still readable. > > Thanks, > > Ilya > > > Ilya Dryomov (9): > rbd: introduce rbd_is_snap() > rbd: introduce RBD_DEV_FLAG_READONLY > rbd: treat images mapped read-only seriously > rbd: disallow read-write partitions on images mapped read-only > rbd: don't acquire exclusive lock for read-only mappings > rbd: don't establish watch for read-only mappings > rbd: remove snapshot existence validation code > rbd: don't query snapshot features > rbd: ask for a weaker incompat mask for read-only mappings > > drivers/block/rbd.c | 203 ++++++++++++++++++++------------------------ > 1 file changed, 93 insertions(+), 110 deletions(-) >
On Tue, Nov 19, 2019 at 9:50 AM Dongsheng Yang <dongsheng.yang@easystack.cn> wrote: > > > Hi Ilya, > > On 11/18/2019 09:38 PM, Ilya Dryomov wrote: > > Hello, > > > > This series makes read-only mappings compatible with read-only caps: > > we no longer establish a watch, > > Although this is true in userspace librbd, I think that's wired: when > there is someone is reading this image, it can be removed. And the > reader will get all zero for later reads. > > What about register a watcher but always ack for notifications? Then > we can prevent removing from image being reading. We can't register a watch because it is a write operation on the OSD and we want read-only mappings to be usable with read-only OSD caps: $ ceph auth add client.ro ... osd 'profile rbd-read-only' $ sudo rbd map --user ro -o ro ... Further, while returning zeros if an image or a snapshot is removed is bad, a watch isn't a good solution. It can be lost, and even when it's there it's still racy. See the description of patch 7. Thanks, Ilya
On 11/19/2019 07:59 PM, Ilya Dryomov wrote: > On Tue, Nov 19, 2019 at 9:50 AM Dongsheng Yang > <dongsheng.yang@easystack.cn> wrote: >> >> Hi Ilya, >> >> On 11/18/2019 09:38 PM, Ilya Dryomov wrote: >>> Hello, >>> >>> This series makes read-only mappings compatible with read-only caps: >>> we no longer establish a watch, >> Although this is true in userspace librbd, I think that's wired: when >> there is someone is reading this image, it can be removed. And the >> reader will get all zero for later reads. >> >> What about register a watcher but always ack for notifications? Then >> we can prevent removing from image being reading. > We can't register a watch because it is a write operation on the OSD > and we want read-only mappings to be usable with read-only OSD caps: > > $ ceph auth add client.ro ... osd 'profile rbd-read-only' > $ sudo rbd map --user ro -o ro .. > > Further, while returning zeros if an image or a snapshot is removed is > bad, a watch isn't a good solution. It can be lost, and even when it's > there it's still racy. See the description of patch 7 Right, it's not that easy. Maybe we need another series patches to improve it. I am okey for it now, librbd is working in the same way. Thanx > > Thanks, > > Ilya >
On Tue, Nov 19, 2019 at 1:11 PM Dongsheng Yang <dongsheng.yang@easystack.cn> wrote: > > > > On 11/19/2019 07:59 PM, Ilya Dryomov wrote: > > On Tue, Nov 19, 2019 at 9:50 AM Dongsheng Yang > > <dongsheng.yang@easystack.cn> wrote: > >> > >> Hi Ilya, > >> > >> On 11/18/2019 09:38 PM, Ilya Dryomov wrote: > >>> Hello, > >>> > >>> This series makes read-only mappings compatible with read-only caps: > >>> we no longer establish a watch, > >> Although this is true in userspace librbd, I think that's wired: when > >> there is someone is reading this image, it can be removed. And the > >> reader will get all zero for later reads. > >> > >> What about register a watcher but always ack for notifications? Then > >> we can prevent removing from image being reading. > > We can't register a watch because it is a write operation on the OSD > > and we want read-only mappings to be usable with read-only OSD caps: > > > > $ ceph auth add client.ro ... osd 'profile rbd-read-only' > > $ sudo rbd map --user ro -o ro .. > > > > Further, while returning zeros if an image or a snapshot is removed is > > bad, a watch isn't a good solution. It can be lost, and even when it's > > there it's still racy. See the description of patch 7 > > > Right, it's not that easy. Maybe we need another series patches to > improve it. Yeah, just watching a header as it is is not going to do it. Thanks for the review! Ilya
Hello, This series makes read-only mappings compatible with read-only caps: we no longer establish a watch, acquire header and object map locks, etc. In addition, because images mapped read-only can no longer be flipped to read-write, we allow read-only mappings with unsupported features, as long as the image is still readable. Thanks, Ilya Ilya Dryomov (9): rbd: introduce rbd_is_snap() rbd: introduce RBD_DEV_FLAG_READONLY rbd: treat images mapped read-only seriously rbd: disallow read-write partitions on images mapped read-only rbd: don't acquire exclusive lock for read-only mappings rbd: don't establish watch for read-only mappings rbd: remove snapshot existence validation code rbd: don't query snapshot features rbd: ask for a weaker incompat mask for read-only mappings drivers/block/rbd.c | 203 ++++++++++++++++++++------------------------ 1 file changed, 93 insertions(+), 110 deletions(-)