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       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                 :            :  */
      22                 :            : loff_t
      23                 :          0 : iomap_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                 :          0 :         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                 :          0 :         ret = ops->iomap_begin(inode, pos, length, flags, &iomap);
      42                 :          0 :         if (ret)
      43                 :            :                 return ret;
      44                 :          0 :         if (WARN_ON(iomap.offset > pos))
      45                 :            :                 return -EIO;
      46                 :          0 :         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                 :          0 :         if (iomap.offset + iomap.length < pos + length)
      54                 :          0 :                 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                 :          0 :         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                 :          0 :         if (ops->iomap_end) {
      68                 :          0 :                 ret = ops->iomap_end(inode, pos, length,
      69                 :          0 :                                      written > 0 ? written : 0,
      70                 :            :                                      flags, &iomap);
      71                 :            :         }
      72                 :            : 
      73                 :          0 :         return written ? written : ret;
      74                 :            : }