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7bd43cc79c
With the development of flash-based storage devices, we can quickly
write zeros to SSDs using the WRITE_ZERO command if the devices do not
actually write physical zeroes to the media. Therefore, we can use this
command to quickly preallocate a real all-zero file with written
extents. This approach should be beneficial for subsequent pure
overwriting within this file, as it can save on block allocation and,
consequently, significant metadata changes, which should greatly improve
overwrite performance on certain filesystems.
Therefore, introduce a new operation FALLOC_FL_WRITE_ZEROES to
fallocate. This flag is used to convert a specified range of a file to
zeros by issuing a zeroing operation. Blocks should be allocated for the
regions that span holes in the file, and the entire range is converted
to written extents. If the underlying device supports the actual offload
write zeroes command, the process of zeroing out operation can be
accelerated. If it does not, we currently don't prevent the file system
from writing actual zeros to the device. This provides users with a new
method to quickly generate a zeroed file, users no longer need to write
zero data to create a file with written extents.
Users can determine whether a disk supports the unmap write zeroes
feature through querying this sysfs interface:
/sys/block/<disk>/queue/write_zeroes_unmap_max_hw_bytes
Users can also enable or disable the unmap write zeroes operation
through this sysfs interface:
/sys/block/<disk>/queue/write_zeroes_unmap_max_bytes
Finally, this flag cannot be specified in conjunction with the
FALLOC_FL_KEEP_SIZE since allocating written extents beyond file EOF is
not permitted. In addition, filesystems that always require out-of-place
writes should not support this flag since they still need to allocated
new blocks during subsequent overwrites.
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/20250619111806.3546162-7-yi.zhang@huaweicloud.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
99 lines
4.4 KiB
C
99 lines
4.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _UAPI_FALLOC_H_
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#define _UAPI_FALLOC_H_
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#define FALLOC_FL_ALLOCATE_RANGE 0x00 /* allocate range */
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#define FALLOC_FL_KEEP_SIZE 0x01 /* default is extend size */
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#define FALLOC_FL_PUNCH_HOLE 0x02 /* de-allocates range */
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#define FALLOC_FL_NO_HIDE_STALE 0x04 /* reserved codepoint */
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/*
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* FALLOC_FL_COLLAPSE_RANGE is used to remove a range of a file
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* without leaving a hole in the file. The contents of the file beyond
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* the range being removed is appended to the start offset of the range
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* being removed (i.e. the hole that was punched is "collapsed"),
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* resulting in a file layout that looks like the range that was
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* removed never existed. As such collapsing a range of a file changes
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* the size of the file, reducing it by the same length of the range
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* that has been removed by the operation.
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*
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* Different filesystems may implement different limitations on the
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* granularity of the operation. Most will limit operations to
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* filesystem block size boundaries, but this boundary may be larger or
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* smaller depending on the filesystem and/or the configuration of the
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* filesystem or file.
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*
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* Attempting to collapse a range that crosses the end of the file is
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* considered an illegal operation - just use ftruncate(2) if you need
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* to collapse a range that crosses EOF.
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*/
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#define FALLOC_FL_COLLAPSE_RANGE 0x08
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/*
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* FALLOC_FL_ZERO_RANGE is used to convert a range of file to zeros preferably
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* without issuing data IO. Blocks should be preallocated for the regions that
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* span holes in the file, and the entire range is preferable converted to
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* unwritten extents - even though file system may choose to zero out the
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* extent or do whatever which will result in reading zeros from the range
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* while the range remains allocated for the file.
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*
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* This can be also used to preallocate blocks past EOF in the same way as
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* with fallocate. Flag FALLOC_FL_KEEP_SIZE should cause the inode
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* size to remain the same.
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*/
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#define FALLOC_FL_ZERO_RANGE 0x10
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/*
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* FALLOC_FL_INSERT_RANGE is use to insert space within the file size without
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* overwriting any existing data. The contents of the file beyond offset are
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* shifted towards right by len bytes to create a hole. As such, this
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* operation will increase the size of the file by len bytes.
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*
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* Different filesystems may implement different limitations on the granularity
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* of the operation. Most will limit operations to filesystem block size
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* boundaries, but this boundary may be larger or smaller depending on
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* the filesystem and/or the configuration of the filesystem or file.
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*
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* Attempting to insert space using this flag at OR beyond the end of
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* the file is considered an illegal operation - just use ftruncate(2) or
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* fallocate(2) with mode 0 for such type of operations.
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*/
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#define FALLOC_FL_INSERT_RANGE 0x20
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/*
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* FALLOC_FL_UNSHARE_RANGE is used to unshare shared blocks within the
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* file size without overwriting any existing data. The purpose of this
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* call is to preemptively reallocate any blocks that are subject to
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* copy-on-write.
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*
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* Different filesystems may implement different limitations on the
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* granularity of the operation. Most will limit operations to filesystem
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* block size boundaries, but this boundary may be larger or smaller
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* depending on the filesystem and/or the configuration of the filesystem
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* or file.
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*
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* This flag can only be used with allocate-mode fallocate, which is
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* to say that it cannot be used with the punch, zero, collapse, or
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* insert range modes.
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*/
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#define FALLOC_FL_UNSHARE_RANGE 0x40
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/*
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* FALLOC_FL_WRITE_ZEROES zeroes a specified file range in such a way that
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* subsequent writes to that range do not require further changes to the file
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* mapping metadata. This flag is beneficial for subsequent pure overwriting
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* within this range, as it can save on block allocation and, consequently,
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* significant metadata changes. Therefore, filesystems that always require
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* out-of-place writes should not support this flag.
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*
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* Different filesystems may implement different limitations on the
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* granularity of the zeroing operation. Most will preferably be accelerated
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* by submitting write zeroes command if the backing storage supports, which
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* may not physically write zeros to the media.
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*
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* This flag cannot be specified in conjunction with the FALLOC_FL_KEEP_SIZE.
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*/
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#define FALLOC_FL_WRITE_ZEROES 0x80
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#endif /* _UAPI_FALLOC_H_ */
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