LXR linux/fs/iomap/apply.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Copyright (C) 2010 Red Hat, Inc.
   4 * Copyright (c) 2016-2018 Christoph Hellwig.
   5 */
   6#include <linux/module.h>
   7#include <linux/compiler.h>
   8#include <linux/fs.h>
   9#include <linux/iomap.h>
  10
  11/*
  12 * Execute a iomap write on a segment of the mapping that spans a
  13 * contiguous range of pages that have identical block mapping state.
  14 *
  15 * This avoids the need to map pages individually, do individual allocations
  16 * for each page and most importantly avoid the need for filesystem specific
  17 * locking per page. Instead, all the operations are amortised over the entire
  18 * range of pages. It is assumed that the filesystems will lock whatever
  19 * resources they require in the iomap_begin call, and release them in the
  20 * iomap_end call.
  21 */
  22loff_t
  23iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
  24                const struct iomap_ops *ops, void *data, iomap_actor_t actor)
  25{
  26        struct iomap iomap = { 0 };
  27        loff_t written = 0, ret;
  28
  29        /*
  30         * Need to map a range from start position for length bytes. This can
  31         * span multiple pages - it is only guaranteed to return a range of a
  32         * single type of pages (e.g. all into a hole, all mapped or all
  33         * unwritten). Failure at this point has nothing to undo.
  34         *
  35         * If allocation is required for this range, reserve the space now so
  36         * that the allocation is guaranteed to succeed later on. Once we copy
  37         * the data into the page cache pages, then we cannot fail otherwise we
  38         * expose transient stale data. If the reserve fails, we can safely
  39         * back out at this point as there is nothing to undo.
  40         */
  41        ret = ops->iomap_begin(inode, pos, length, flags, &iomap);
  42        if (ret)
  43                return ret;
  44        if (WARN_ON(iomap.offset > pos))
  45                return -EIO;
  46        if (WARN_ON(iomap.length == 0))
  47                return -EIO;
  48
  49        /*
  50         * Cut down the length to the one actually provided by the filesystem,
  51         * as it might not be able to give us the whole size that we requested.
  52         */
  53        if (iomap.offset + iomap.length < pos + length)
  54                length = iomap.offset + iomap.length - pos;
  55
  56        /*
  57         * Now that we have guaranteed that the space allocation will succeed.
  58         * we can do the copy-in page by page without having to worry about
  59         * failures exposing transient data.
  60         */
  61        written = actor(inode, pos, length, data, &iomap);
  62
  63        /*
  64         * Now the data has been copied, commit the range we've copied.  This
  65         * should not fail unless the filesystem has had a fatal error.
  66         */
  67        if (ops->iomap_end) {
  68                ret = ops->iomap_end(inode, pos, length,
  69                                     written > 0 ? written : 0,
  70                                     flags, &iomap);
  71        }
  72
  73        return written ? written : ret;
  74}
  75