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