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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2010 Red Hat, Inc.
* Copyright (c) 2016-2021 Christoph Hellwig.
*/
#include <linux/module.h>
#include <linux/compiler.h>
#include <linux/fs.h>
#include <linux/iomap.h>
#include "trace.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;
trace_iomap_apply(inode, pos, length, flags, ops, actor, _RET_IP_);
/*
* 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)) {
written = -EIO;
goto out;
}
if (WARN_ON(iomap.length == 0)) {
written = -EIO;
goto out;
}
trace_iomap_apply_dstmap(inode, &iomap);
if (srcmap.type != IOMAP_HOLE)
trace_iomap_apply_srcmap(inode, &srcmap);
/*
* 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);
out:
/*
* 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;
}
static inline int iomap_iter_advance(struct iomap_iter *iter)
{
/* handle the previous iteration (if any) */
if (iter->iomap.length) {
if (iter->processed <= 0)
return iter->processed;
if (WARN_ON_ONCE(iter->processed > iomap_length(iter)))
return -EIO;
iter->pos += iter->processed;
iter->len -= iter->processed;
if (!iter->len)
return 0;
}
/* clear the state for the next iteration */
iter->processed = 0;
memset(&iter->iomap, 0, sizeof(iter->iomap));
memset(&iter->srcmap, 0, sizeof(iter->srcmap));
return 1;
}
static inline void iomap_iter_done(struct iomap_iter *iter)
{
WARN_ON_ONCE(iter->iomap.offset > iter->pos);
WARN_ON_ONCE(iter->iomap.length == 0);
WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos);
trace_iomap_iter_dstmap(iter->inode, &iter->iomap);
if (iter->srcmap.type != IOMAP_HOLE)
trace_iomap_iter_srcmap(iter->inode, &iter->srcmap);
}
/**
* iomap_iter - iterate over a ranges in a file
* @iter: iteration structue
* @ops: iomap ops provided by the file system
*
* Iterate over filesystem-provided space mappings for the provided file range.
*
* This function handles cleanup of resources acquired for iteration when the
* filesystem indicates there are no more space mappings, which means that this
* function must be called in a loop that continues as long it returns a
* positive value. If 0 or a negative value is returned, the caller must not
* return to the loop body. Within a loop body, there are two ways to break out
* of the loop body: leave @iter.processed unchanged, or set it to a negative
* errno.
*/
int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
{
int ret;
if (iter->iomap.length && ops->iomap_end) {
ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter),
iter->processed > 0 ? iter->processed : 0,
iter->flags, &iter->iomap);
if (ret < 0 && !iter->processed)
return ret;
}
trace_iomap_iter(iter, ops, _RET_IP_);
ret = iomap_iter_advance(iter);
if (ret <= 0)
return ret;
ret = ops->iomap_begin(iter->inode, iter->pos, iter->len, iter->flags,
&iter->iomap, &iter->srcmap);
if (ret < 0)
return ret;
iomap_iter_done(iter);
return 1;
}
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