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vfs: add a FALLOC_FL_UNSHARE mode to fallocate to unshare a range of blocks

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Add a new fallocate mode flag that explicitly unshares blocks on
filesystems that support such features.  The new flag can only
be used with an allocate-mode fallocate call.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Darrick J. Wong 2016-10-03 09:11:14 -07:00
parent 0a6eab8bd4
commit 71be6b4942
3 changed files with 25 additions and 1 deletions
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18
include/uapi/linux/falloc.h
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@ -58,4 +58,22 @@
*/
#define FALLOC_FL_INSERT_RANGE 0x20
/*
* FALLOC_FL_UNSHARE_RANGE is used to unshare shared blocks within the
* file size without overwriting any existing data. The purpose of this
* call is to preemptively reallocate any blocks that are subject to
* copy-on-write.
*
* Different filesystems may implement different limitations on the
* granularity of the operation. Most will limit operations to filesystem
* block size boundaries, but this boundary may be larger or smaller
* depending on the filesystem and/or the configuration of the filesystem
* or file.
*
* This flag can only be used with allocate-mode fallocate, which is
* to say that it cannot be used with the punch, zero, collapse, or
* insert range modes.
*/
#define FALLOC_FL_UNSHARE_RANGE 0x40
#endif /* _UAPI_FALLOC_H_ */