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#include "trace.h" 11 12/* 13 * Execute a iomap write on a segment of the mapping that spans a 14 * contiguous range of pages that have identical block mapping state. 15 * 16 * This avoids the need to map pages individually, do individual allocations 17 * for each page and most importantly avoid the need for filesystem specific 18 * locking per page. Instead, all the operations are amortised over the entire 19 * range of pages. It is assumed that the filesystems will lock whatever 20 * resources they require in the iomap_begin call, and release them in the 21 * iomap_end call. 22 */ 23loff_t 24iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags, 25 const struct iomap_ops *ops, void *data, iomap_actor_t actor) 26{ 27 struct iomap iomap = { .type = IOMAP_HOLE }; 28 struct iomap srcmap = { .type = IOMAP_HOLE }; 29 loff_t written = 0, ret; 30 u64 end; 31 32 trace_iomap_apply(inode, pos, length, flags, ops, actor, _RET_IP_); 33 34 /* 35 * Need to map a range from start position for length bytes. This can 36 * span multiple pages - it is only guaranteed to return a range of a 37 * single type of pages (e.g. all into a hole, all mapped or all 38 * unwritten). Failure at this point has nothing to undo. 39 * 40 * If allocation is required for this range, reserve the space now so 41 * that the allocation is guaranteed to succeed later on. Once we copy 42 * the data into the page cache pages, then we cannot fail otherwise we 43 * expose transient stale data. If the reserve fails, we can safely 44 * back out at this point as there is nothing to undo. 45 */ 46 ret = ops->iomap_begin(inode, pos, length, flags, &iomap, &srcmap); 47 if (ret) 48 return ret; 49 if (WARN_ON(iomap.offset > pos)) { 50 written = -EIO; 51 goto out; 52 } 53 if (WARN_ON(iomap.length == 0)) { 54 written = -EIO; 55 goto out; 56 } 57 58 trace_iomap_apply_dstmap(inode, &iomap); 59 if (srcmap.type != IOMAP_HOLE) 60 trace_iomap_apply_srcmap(inode, &srcmap); 61 62 /* 63 * Cut down the length to the one actually provided by the filesystem, 64 * as it might not be able to give us the whole size that we requested. 65 */ 66 end = iomap.offset + iomap.length; 67 if (srcmap.type != IOMAP_HOLE) 68 end = min(end, srcmap.offset + srcmap.length); 69 if (pos + length > end) 70 length = end - pos; 71 72 /* 73 * Now that we have guaranteed that the space allocation will succeed, 74 * we can do the copy-in page by page without having to worry about 75 * failures exposing transient data. 76 * 77 * To support COW operations, we read in data for partially blocks from 78 * the srcmap if the file system filled it in. In that case we the 79 * length needs to be limited to the earlier of the ends of the iomaps. 80 * If the file system did not provide a srcmap we pass in the normal 81 * iomap into the actors so that they don't need to have special 82 * handling for the two cases. 83 */ 84 written = actor(inode, pos, length, data, &iomap, 85 srcmap.type != IOMAP_HOLE ? &srcmap : &iomap); 86 87out: 88 /* 89 * Now the data has been copied, commit the range we've copied. This 90 * should not fail unless the filesystem has had a fatal error. 91 */ 92 if (ops->iomap_end) { 93 ret = ops->iomap_end(inode, pos, length, 94 written > 0 ? written : 0, 95 flags, &iomap); 96 } 97 98 return written ? written : ret; 99} 100