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ext4: refactor punch hole code

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Move common code in ext4_ind_punch_hole() and ext4_ext_punch_hole()
into ext4_punch_hole().  This saves over 150 lines of code.

This also fixes a potential bug when the punch_hole() code is racing
against indirect-to-extents or extents-to-indirect migation.  We are
currently using i_mutex to protect against changes to the inode flag;
specifically, the append-only, immutable, and extents inode flags.  So
we need to take i_mutex before deciding whether to use the
extents-specific or indirect-specific punch_hole code.

Also, there was a missing call to ext4_inode_block_unlocked_dio() in
the indirect punch codepath.  This was added in commit 02d262dffc
to block DIO readers racing against the punch operation in the
codepath for extent-mapped inodes, but it was missing for
indirect-block mapped inodes.  One of the advantages of refactoring
the code is that it makes such oversights much less likely.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o
2013-04-03 12:45:17 -04:00
parent 781f143ea0
commit 26a4c0c6cc
4 changed files with 183 additions and 347 deletions
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180
fs/ext4/inode.c
View File

@ -3566,20 +3566,190 @@ int ext4_can_truncate(struct inode *inode)
int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
{
struct inode *inode = file_inode(file);
struct super_block *sb = inode->i_sb;
ext4_lblk_t first_block, stop_block;
struct address_space *mapping = inode->i_mapping;
loff_t first_page, last_page, page_len;
loff_t first_page_offset, last_page_offset;
handle_t *handle;
unsigned int credits;
int ret = 0;
if (!S_ISREG(inode->i_mode))
return -EOPNOTSUPP;
if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
return ext4_ind_punch_hole(file, offset, length);
if (EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) {
if (EXT4_SB(sb)->s_cluster_ratio > 1) {
/* TODO: Add support for bigalloc file systems */
return -EOPNOTSUPP;
}
trace_ext4_punch_hole(inode, offset, length);
return ext4_ext_punch_hole(file, offset, length);
/*
* Write out all dirty pages to avoid race conditions
* Then release them.
*/
if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
ret = filemap_write_and_wait_range(mapping, offset,
offset + length - 1);
if (ret)
return ret;
}
mutex_lock(&inode->i_mutex);
/* It's not possible punch hole on append only file */
if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) {
ret = -EPERM;
goto out_mutex;
}
if (IS_SWAPFILE(inode)) {
ret = -ETXTBSY;
goto out_mutex;
}
/* No need to punch hole beyond i_size */
if (offset >= inode->i_size)
goto out_mutex;
/*
* If the hole extends beyond i_size, set the hole
* to end after the page that contains i_size
*/
if (offset + length > inode->i_size) {
length = inode->i_size +
PAGE_CACHE_SIZE - (inode->i_size & (PAGE_CACHE_SIZE - 1)) -
offset;
}
first_page = (offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
last_page = (offset + length) >> PAGE_CACHE_SHIFT;
first_page_offset = first_page << PAGE_CACHE_SHIFT;
last_page_offset = last_page << PAGE_CACHE_SHIFT;
/* Now release the pages */
if (last_page_offset > first_page_offset) {
truncate_pagecache_range(inode, first_page_offset,
last_page_offset - 1);
}
/* Wait all existing dio workers, newcomers will block on i_mutex */
ext4_inode_block_unlocked_dio(inode);
ret = ext4_flush_unwritten_io(inode);
if (ret)
goto out_dio;
inode_dio_wait(inode);
if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
credits = ext4_writepage_trans_blocks(inode);
else
credits = ext4_blocks_for_truncate(inode);
handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
ext4_std_error(sb, ret);
goto out_dio;
}
/*
* Now we need to zero out the non-page-aligned data in the
* pages at the start and tail of the hole, and unmap the
* buffer heads for the block aligned regions of the page that
* were completely zeroed.
*/
if (first_page > last_page) {
/*
* If the file space being truncated is contained
* within a page just zero out and unmap the middle of
* that page
*/
ret = ext4_discard_partial_page_buffers(handle,
mapping, offset, length, 0);
if (ret)
goto out_stop;
} else {
/*
* zero out and unmap the partial page that contains
* the start of the hole
*/
page_len = first_page_offset - offset;
if (page_len > 0) {
ret = ext4_discard_partial_page_buffers(handle, mapping,
offset, page_len, 0);
if (ret)
goto out_stop;
}
/*
* zero out and unmap the partial page that contains
* the end of the hole
*/
page_len = offset + length - last_page_offset;
if (page_len > 0) {
ret = ext4_discard_partial_page_buffers(handle, mapping,
last_page_offset, page_len, 0);
if (ret)
goto out_stop;
}
}
/*
* If i_size is contained in the last page, we need to
* unmap and zero the partial page after i_size
*/
if (inode->i_size >> PAGE_CACHE_SHIFT == last_page &&
inode->i_size % PAGE_CACHE_SIZE != 0) {
page_len = PAGE_CACHE_SIZE -
(inode->i_size & (PAGE_CACHE_SIZE - 1));
if (page_len > 0) {
ret = ext4_discard_partial_page_buffers(handle,
mapping, inode->i_size, page_len, 0);
if (ret)
goto out_stop;
}
}
first_block = (offset + sb->s_blocksize - 1) >>
EXT4_BLOCK_SIZE_BITS(sb);
stop_block = (offset + length) >> EXT4_BLOCK_SIZE_BITS(sb);
/* If there are no blocks to remove, return now */
if (first_block >= stop_block)
goto out_stop;
down_write(&EXT4_I(inode)->i_data_sem);
ext4_discard_preallocations(inode);
ret = ext4_es_remove_extent(inode, first_block,
stop_block - first_block);
if (ret) {
up_write(&EXT4_I(inode)->i_data_sem);
goto out_stop;
}
if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
ret = ext4_ext_remove_space(inode, first_block,
stop_block - 1);
else
ret = ext4_free_hole_blocks(handle, inode, first_block,
stop_block);
ext4_discard_preallocations(inode);
if (IS_SYNC(inode))
ext4_handle_sync(handle);
up_write(&EXT4_I(inode)->i_data_sem);
inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
ext4_mark_inode_dirty(handle, inode);
out_stop:
ext4_journal_stop(handle);
out_dio:
ext4_inode_resume_unlocked_dio(inode);
out_mutex:
mutex_unlock(&inode->i_mutex);
return ret;
}
/*