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fs: introduce new truncate sequence

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Introduce a new truncate calling sequence into fs/mm subsystems. Rather than
setattr > vmtruncate > truncate, have filesystems call their truncate sequence
from ->setattr if filesystem specific operations are required. vmtruncate is
deprecated, and truncate_pagecache and inode_newsize_ok helpers introduced
previously should be used.

simple_setattr is introduced for simple in-ram filesystems to implement
the new truncate sequence. Eventually all filesystems should be converted
to implement a setattr, and the default code in notify_change should go
away.

simple_setsize is also introduced to perform just the ATTR_SIZE portion
of simple_setattr (ie. changing i_size and trimming pagecache).

To implement the new truncate sequence:
- filesystem specific manipulations (eg freeing blocks) must be done in
  the setattr method rather than ->truncate.
- vmtruncate can not be used by core code to trim blocks past i_size in
  the event of write failure after allocation, so this must be performed
  in the fs code.
- convert usage of helpers block_write_begin, nobh_write_begin,
  cont_write_begin, and *blockdev_direct_IO* to use _newtrunc postfixed
  variants. These avoid calling vmtruncate to trim blocks (see previous).
- inode_setattr should not be used. generic_setattr is a new function
  to be used to copy simple attributes into the generic inode.
- make use of the better opportunity to handle errors with the new sequence.

Big problem with the previous calling sequence: the filesystem is not called
until i_size has already changed.  This means it is not allowed to fail the
call, and also it does not know what the previous i_size was. Also, generic
code calling vmtruncate to truncate allocated blocks in case of error had
no good way to return a meaningful error (or, for example, atomically handle
block deallocation).

Cc: Christoph Hellwig <hch@lst.de>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
npiggin@suse.de 2010-05-27 01:05:33 +10:00 • committed by Al Viro
parent 7000d3c424
commit 7bb46a6734
8 changed files with 300 additions and 63 deletions
Download patch file Download diff file Expand all files Collapse all files

123
fs/buffer.c
View file

@ -1949,14 +1949,11 @@ static int __block_commit_write(struct inode *inode, struct page *page,
}
/*
* block_write_begin takes care of the basic task of block allocation and
* bringing partial write blocks uptodate first.
*
* If *pagep is not NULL, then block_write_begin uses the locked page
* at *pagep rather than allocating its own. In this case, the page will
* not be unlocked or deallocated on failure.
* Filesystems implementing the new truncate sequence should use the
* _newtrunc postfix variant which won't incorrectly call vmtruncate.
* The filesystem needs to handle block truncation upon failure.
*/
int block_write_begin(struct file *file, struct address_space *mapping,
int block_write_begin_newtrunc(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block)
@ -1992,20 +1989,50 @@ int block_write_begin(struct file *file, struct address_space *mapping,
unlock_page(page);
page_cache_release(page);
*pagep = NULL;
/*
* prepare_write() may have instantiated a few blocks
* outside i_size. Trim these off again. Don't need
* i_size_read because we hold i_mutex.
*/
if (pos + len > inode->i_size)
vmtruncate(inode, inode->i_size);
}
}
out:
return status;
}
EXPORT_SYMBOL(block_write_begin_newtrunc);
/*
* block_write_begin takes care of the basic task of block allocation and
* bringing partial write blocks uptodate first.
*
* If *pagep is not NULL, then block_write_begin uses the locked page
* at *pagep rather than allocating its own. In this case, the page will
* not be unlocked or deallocated on failure.
*/
int block_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block)
{
int ret;
ret = block_write_begin_newtrunc(file, mapping, pos, len, flags,
pagep, fsdata, get_block);
/*
* prepare_write() may have instantiated a few blocks
* outside i_size. Trim these off again. Don't need
* i_size_read because we hold i_mutex.
*
* Filesystems which pass down their own page also cannot
* call into vmtruncate here because it would lead to lock
* inversion problems (*pagep is locked). This is a further
* example of where the old truncate sequence is inadequate.
*/
if (unlikely(ret) && *pagep == NULL) {
loff_t isize = mapping->host->i_size;
if (pos + len > isize)
vmtruncate(mapping->host, isize);
}
return ret;
}
EXPORT_SYMBOL(block_write_begin);
int block_write_end(struct file *file, struct address_space *mapping,
@ -2324,7 +2351,7 @@ out:
* For moronic filesystems that do not allow holes in file.
* We may have to extend the file.
*/
int cont_write_begin(struct file *file, struct address_space *mapping,
int cont_write_begin_newtrunc(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block, loff_t *bytes)
@ -2345,11 +2372,30 @@ int cont_write_begin(struct file *file, struct address_space *mapping,
}
*pagep = NULL;
err = block_write_begin(file, mapping, pos, len,
err = block_write_begin_newtrunc(file, mapping, pos, len,
flags, pagep, fsdata, get_block);
out:
return err;
}
EXPORT_SYMBOL(cont_write_begin_newtrunc);
int cont_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block, loff_t *bytes)
{
int ret;
ret = cont_write_begin_newtrunc(file, mapping, pos, len, flags,
pagep, fsdata, get_block, bytes);
if (unlikely(ret)) {
loff_t isize = mapping->host->i_size;
if (pos + len > isize)
vmtruncate(mapping->host, isize);
}
return ret;
}
EXPORT_SYMBOL(cont_write_begin);
int block_prepare_write(struct page *page, unsigned from, unsigned to,
@ -2381,7 +2427,7 @@ EXPORT_SYMBOL(block_commit_write);
*
* We are not allowed to take the i_mutex here so we have to play games to
* protect against truncate races as the page could now be beyond EOF. Because
* vmtruncate() writes the inode size before removing pages, once we have the
* truncate writes the inode size before removing pages, once we have the
* page lock we can determine safely if the page is beyond EOF. If it is not
* beyond EOF, then the page is guaranteed safe against truncation until we
* unlock the page.
@ -2464,10 +2510,11 @@ static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
}
/*
* On entry, the page is fully not uptodate.
* On exit the page is fully uptodate in the areas outside (from,to)
* Filesystems implementing the new truncate sequence should use the
* _newtrunc postfix variant which won't incorrectly call vmtruncate.
* The filesystem needs to handle block truncation upon failure.
*/
int nobh_write_begin(struct file *file, struct address_space *mapping,
int nobh_write_begin_newtrunc(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block)
@ -2500,8 +2547,8 @@ int nobh_write_begin(struct file *file, struct address_space *mapping,
unlock_page(page);
page_cache_release(page);
*pagep = NULL;
return block_write_begin(file, mapping, pos, len, flags, pagep,
fsdata, get_block);
return block_write_begin_newtrunc(file, mapping, pos, len,
flags, pagep, fsdata, get_block);
}
if (PageMappedToDisk(page))
@ -2605,8 +2652,34 @@ out_release:
page_cache_release(page);
*pagep = NULL;
if (pos + len > inode->i_size)
vmtruncate(inode, inode->i_size);
return ret;
}
EXPORT_SYMBOL(nobh_write_begin_newtrunc);
/*
* On entry, the page is fully not uptodate.
* On exit the page is fully uptodate in the areas outside (from,to)
*/
int nobh_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata,
get_block_t *get_block)
{
int ret;
ret = nobh_write_begin_newtrunc(file, mapping, pos, len, flags,
pagep, fsdata, get_block);
/*
* prepare_write() may have instantiated a few blocks
* outside i_size. Trim these off again. Don't need
* i_size_read because we hold i_mutex.
*/
if (unlikely(ret)) {
loff_t isize = mapping->host->i_size;
if (pos + len > isize)
vmtruncate(mapping->host, isize);
}
return ret;
}