Commit afa2db2f authored Jun 24, 2015 by Josef Bacik Committed by Linus Torvalds Jun 24, 2015

tmpfs: truncate prealloc blocks past i_size



One of the rocksdb people noticed that when you do something like this

    fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, 10M)
    pwrite(fd, buf, 5M, 0)
    ftruncate(5M)

on tmpfs, the file would still take up 10M: which led to super fun
issues because we were getting ENOSPC before we thought we should be
getting ENOSPC.  This patch fixes the problem, and mirrors what all the
other fs'es do (and was agreed to be the correct behaviour at LSF).

I tested it locally to make sure it worked properly with the following

    xfs_io -f -c "falloc -k 0 10M" -c "pwrite 0 5M" -c "truncate 5M" file

Without the patch we have "Blocks: 20480", with the patch we have the
correct value of "Blocks: 10240".

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c435a390

mm/shmem.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -569,7 +569,7 @@ static int shmem_setattr(struct dentry dentry, struct iattr attr)
		i_size_write(inode, newsize);
		inode->i_ctime = inode->i_mtime = CURRENT_TIME;
		}
		if (newsize < oldsize) {
		if (newsize <= oldsize) {
		loff_t holebegin = round_up(newsize, PAGE_SIZE);
		unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
		shmem_truncate_range(inode, newsize, (loff_t)-1);

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