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ceph: document ioctls 

...after some prodding by Christoph.

Signed-off-by: Sage Weil <sage@newdream.net>
This commit is contained in:
Sage Weil 2011-08-04 15:41:37 -07:00
parent 0d66a487c1
commit 6a8ea4706a
1 changed files with 54 additions and 1 deletions
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55
fs/ceph/ioctl.h
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@ -6,7 +6,31 @@
#define CEPH_IOCTL_MAGIC 0x97
/* just use u64 to align sanely on all archs */
/*
* CEPH_IOC_GET_LAYOUT - get file layout or dir layout policy
* CEPH_IOC_SET_LAYOUT - set file layout
* CEPH_IOC_SET_LAYOUT_POLICY - set dir layout policy
*
* The file layout specifies how file data is striped over objects in
* the distributed object store, which object pool they belong to (if
* it differs from the default), and an optional 'preferred osd' to
* store them on.
*
* Files get a new layout based on the policy set on the containing
* directory or one of its ancestors. The GET_LAYOUT ioctl will let
* you examine the layout for a file or the policy on a directory.
*
* SET_LAYOUT will let you set a layout on a newly created file. This
* only works immediately after the file is created and before any
* data is written to it.
*
* SET_LAYOUT_POLICY will let you set a layout policy (default layout)
* on a directory that will apply to any new files created in that
* directory (or any child directory that doesn't specify a layout of
* its own).
*/
/* use u64 to align sanely on all archs */
struct ceph_ioctl_layout {
__u64 stripe_unit, stripe_count, object_size;
__u64 data_pool;
@ -21,6 +45,8 @@ struct ceph_ioctl_layout {
struct ceph_ioctl_layout)
/*
* CEPH_IOC_GET_DATALOC - get location of file data in the cluster
*
* Extract identity, address of the OSD and object storing a given
* file offset.
*/
@ -39,7 +65,34 @@ struct ceph_ioctl_dataloc {
#define CEPH_IOC_GET_DATALOC _IOWR(CEPH_IOCTL_MAGIC, 3, \
struct ceph_ioctl_dataloc)
/*
* CEPH_IOC_LAZYIO - relax consistency
*
* Normally Ceph switches to synchronous IO when multiple clients have
* the file open (and or more for write). Reads and writes bypass the
* page cache and go directly to the OSD. Setting this flag on a file
* descriptor will allow buffered IO for this file in cases where the
* application knows it won't interfere with other nodes (or doesn't
* care).
*/
#define CEPH_IOC_LAZYIO _IO(CEPH_IOCTL_MAGIC, 4)
/*
* CEPH_IOC_SYNCIO - force synchronous IO
*
* This ioctl sets a file flag that forces the synchronous IO that
* bypasses the page cache, even if it is not necessary. This is
* essentially the opposite behavior of IOC_LAZYIO. This forces the
* same read/write path as a file opened by multiple clients when one
* or more of those clients is opened for write.
*
* Note that this type of sync IO takes a different path than a file
* opened with O_SYNC/D_SYNC (writes hit the page cache and are
* immediately flushed on page boundaries). It is very similar to
* O_DIRECT (writes bypass the page cache) excep that O_DIRECT writes
* are not copied (user page must remain stable) and O_DIRECT writes
* have alignment restrictions (on the buffer and file offset).
*/
#define CEPH_IOC_SYNCIO _IO(CEPH_IOCTL_MAGIC, 5)
#endif