95 строки
3.3 KiB
C
95 строки
3.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2010 Red Hat, Inc.
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* Copyright (c) 2016-2018 Christoph Hellwig.
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*/
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#include <linux/module.h>
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#include <linux/compiler.h>
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#include <linux/fs.h>
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#include <linux/iomap.h>
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#include "trace.h"
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/*
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* Execute a iomap write on a segment of the mapping that spans a
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* contiguous range of pages that have identical block mapping state.
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*
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* This avoids the need to map pages individually, do individual allocations
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* for each page and most importantly avoid the need for filesystem specific
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* locking per page. Instead, all the operations are amortised over the entire
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* range of pages. It is assumed that the filesystems will lock whatever
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* resources they require in the iomap_begin call, and release them in the
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* iomap_end call.
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*/
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loff_t
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iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
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const struct iomap_ops *ops, void *data, iomap_actor_t actor)
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{
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struct iomap iomap = { .type = IOMAP_HOLE };
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struct iomap srcmap = { .type = IOMAP_HOLE };
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loff_t written = 0, ret;
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u64 end;
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trace_iomap_apply(inode, pos, length, flags, ops, actor, _RET_IP_);
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/*
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* Need to map a range from start position for length bytes. This can
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* span multiple pages - it is only guaranteed to return a range of a
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* single type of pages (e.g. all into a hole, all mapped or all
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* unwritten). Failure at this point has nothing to undo.
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*
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* If allocation is required for this range, reserve the space now so
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* that the allocation is guaranteed to succeed later on. Once we copy
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* the data into the page cache pages, then we cannot fail otherwise we
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* expose transient stale data. If the reserve fails, we can safely
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* back out at this point as there is nothing to undo.
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*/
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ret = ops->iomap_begin(inode, pos, length, flags, &iomap, &srcmap);
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if (ret)
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return ret;
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if (WARN_ON(iomap.offset > pos))
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return -EIO;
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if (WARN_ON(iomap.length == 0))
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return -EIO;
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trace_iomap_apply_dstmap(inode, &iomap);
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if (srcmap.type != IOMAP_HOLE)
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trace_iomap_apply_srcmap(inode, &srcmap);
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/*
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* Cut down the length to the one actually provided by the filesystem,
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* as it might not be able to give us the whole size that we requested.
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*/
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end = iomap.offset + iomap.length;
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if (srcmap.type != IOMAP_HOLE)
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end = min(end, srcmap.offset + srcmap.length);
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if (pos + length > end)
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length = end - pos;
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/*
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* Now that we have guaranteed that the space allocation will succeed,
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* we can do the copy-in page by page without having to worry about
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* failures exposing transient data.
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*
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* To support COW operations, we read in data for partially blocks from
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* the srcmap if the file system filled it in. In that case we the
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* length needs to be limited to the earlier of the ends of the iomaps.
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* If the file system did not provide a srcmap we pass in the normal
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* iomap into the actors so that they don't need to have special
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* handling for the two cases.
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*/
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written = actor(inode, pos, length, data, &iomap,
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srcmap.type != IOMAP_HOLE ? &srcmap : &iomap);
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/*
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* Now the data has been copied, commit the range we've copied. This
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* should not fail unless the filesystem has had a fatal error.
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*/
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if (ops->iomap_end) {
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ret = ops->iomap_end(inode, pos, length,
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written > 0 ? written : 0,
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flags, &iomap);
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}
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return written ? written : ret;
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}
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