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 #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  */
  23 loff_t
  24 iomap_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
  87 out:
  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 }