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ceph: document ioctls
...after some prodding by Christoph. Signed-off-by: Sage Weil <sage@newdream.net>
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1 changed files with 54 additions and 1 deletions
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@ -6,7 +6,31 @@
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#define CEPH_IOCTL_MAGIC 0x97
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/* just use u64 to align sanely on all archs */
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/*
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* CEPH_IOC_GET_LAYOUT - get file layout or dir layout policy
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* CEPH_IOC_SET_LAYOUT - set file layout
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* CEPH_IOC_SET_LAYOUT_POLICY - set dir layout policy
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*
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* The file layout specifies how file data is striped over objects in
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* the distributed object store, which object pool they belong to (if
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* it differs from the default), and an optional 'preferred osd' to
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* store them on.
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*
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* Files get a new layout based on the policy set on the containing
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* directory or one of its ancestors. The GET_LAYOUT ioctl will let
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* you examine the layout for a file or the policy on a directory.
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*
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* SET_LAYOUT will let you set a layout on a newly created file. This
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* only works immediately after the file is created and before any
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* data is written to it.
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*
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* SET_LAYOUT_POLICY will let you set a layout policy (default layout)
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* on a directory that will apply to any new files created in that
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* directory (or any child directory that doesn't specify a layout of
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* its own).
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*/
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/* use u64 to align sanely on all archs */
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struct ceph_ioctl_layout {
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__u64 stripe_unit, stripe_count, object_size;
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__u64 data_pool;
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@ -21,6 +45,8 @@ struct ceph_ioctl_layout {
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struct ceph_ioctl_layout)
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/*
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* CEPH_IOC_GET_DATALOC - get location of file data in the cluster
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*
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* Extract identity, address of the OSD and object storing a given
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* file offset.
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*/
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@ -39,7 +65,34 @@ struct ceph_ioctl_dataloc {
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#define CEPH_IOC_GET_DATALOC _IOWR(CEPH_IOCTL_MAGIC, 3, \
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struct ceph_ioctl_dataloc)
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/*
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* CEPH_IOC_LAZYIO - relax consistency
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*
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* Normally Ceph switches to synchronous IO when multiple clients have
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* the file open (and or more for write). Reads and writes bypass the
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* page cache and go directly to the OSD. Setting this flag on a file
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* descriptor will allow buffered IO for this file in cases where the
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* application knows it won't interfere with other nodes (or doesn't
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* care).
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*/
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#define CEPH_IOC_LAZYIO _IO(CEPH_IOCTL_MAGIC, 4)
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/*
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* CEPH_IOC_SYNCIO - force synchronous IO
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*
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* This ioctl sets a file flag that forces the synchronous IO that
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* bypasses the page cache, even if it is not necessary. This is
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* essentially the opposite behavior of IOC_LAZYIO. This forces the
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* same read/write path as a file opened by multiple clients when one
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* or more of those clients is opened for write.
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*
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* Note that this type of sync IO takes a different path than a file
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* opened with O_SYNC/D_SYNC (writes hit the page cache and are
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* immediately flushed on page boundaries). It is very similar to
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* O_DIRECT (writes bypass the page cache) excep that O_DIRECT writes
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* are not copied (user page must remain stable) and O_DIRECT writes
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* have alignment restrictions (on the buffer and file offset).
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*/
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#define CEPH_IOC_SYNCIO _IO(CEPH_IOCTL_MAGIC, 5)
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#endif
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