Date:	Fri, 31 Jan 2014 17:59:01 +0100
From:	Jan Kara <jack@...e.cz>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v5 06/22] Treat XIP like O_DIRECT

On Wed 15-01-14 20:24:24, Matthew Wilcox wrote:
> Instead of separate read and write methods, use the generic AIO
> infrastructure.  In addition to giving us support for AIO, this adds
> the locking between read() and truncate() that was missing.
> 
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@...el.com>
> ---
>  fs/Makefile        |   1 +
>  fs/ext2/file.c     |   6 +-
>  fs/ext2/inode.c    |   7 +-
>  fs/xip.c           | 156 +++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  18 ++++-
>  mm/filemap.c       |   6 +-
>  mm/filemap_xip.c   | 234 -----------------------------------------------------
>  7 files changed, 183 insertions(+), 245 deletions(-)
>  create mode 100644 fs/xip.c
> 
...
> +static ssize_t xip_io(int rw, struct inode *inode, const struct iovec *iov,
> +			loff_t start, loff_t end, unsigned nr_segs,
> +			get_block_t get_block, struct buffer_head *bh)
> +{
> +	ssize_t retval = 0;
> +	unsigned seg = 0;
> +	unsigned len;
> +	unsigned copied = 0;
> +	loff_t offset = start;
> +	loff_t max = start;
> +	void *addr;
> +	bool hole = false;
> +
> +	while (offset < end) {
> +		void __user *buf = iov[seg].iov_base + copied;
> +
> +		if (max == offset) {
> +			sector_t block = offset >> inode->i_blkbits;
> +			long size;
> +			memset(bh, 0, sizeof(*bh));
> +			bh->b_size = ALIGN(end - offset, PAGE_SIZE);
> +			retval = get_block(inode, block, bh, rw == WRITE);
> +			if (retval)
> +				break;
> +			if (buffer_mapped(bh)) {
> +				retval = xip_get_addr(inode, bh, &addr);
> +				if (retval < 0)
> +					break;
> +				addr += offset - (block << inode->i_blkbits);
> +				hole = false;
> +				size = retval;
  I think you are missing here zeroing out partial pages at the head and
the tail of the mapped extent when buffer_new(bh). Dave Chinner found this
in his testing as well I think.

								Honza

> +			} else {
> +				if (rw == WRITE) {
> +					retval = -EIO;
> +					break;
> +				}
> +				addr = NULL;
> +				hole = true;
> +				size = bh->b_size;
> +			}
> +			max = offset + size;
> +		}
> +
> +		len = min_t(unsigned, iov[seg].iov_len - copied, max - offset);
> +
> +		if (rw == WRITE)
> +			len -= __copy_from_user_nocache(addr, buf, len);
> +		else if (!hole)
> +			len -= __copy_to_user(buf, addr, len);
> +		else
> +			len -= __clear_user(buf, len);
> +
> +		if (!len)
> +			break;
> +
> +		offset += len;
> +		copied += len;
> +		if (copied == iov[seg].iov_len) {
> +			seg++;
> +			copied = 0;
> +		}
> +	}
> +
> +	return (offset == start) ? retval : offset - start;
> +}
> +
> +/**
> + * xip_do_io - Perform I/O to an XIP file
> + * @rw: READ to read or WRITE to write
> + * @iocb: The control block for this I/O
> + * @inode: The file which the I/O is directed at
> + * @iov: The user addresses to do I/O from or to
> + * @offset: The file offset where the I/O starts
> + * @nr_segs: The length of the iov array
> + * @get_block: The filesystem method used to translate file offsets to blocks
> + * @end_io: A filesystem callback for I/O completion
> + * @flags: See below
> + *
> + * This function uses the same locking scheme as do_blockdev_direct_IO:
> + * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
> + * caller for writes.  For reads, we take and release the i_mutex ourselves.
> + * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
> + * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
> + * is in progress.
> + */
> +ssize_t xip_do_io(int rw, struct kiocb *iocb, struct inode *inode,
> +		const struct iovec *iov, loff_t offset, unsigned nr_segs,
> +		get_block_t get_block, dio_iodone_t end_io, int flags)
> +{
> +	struct buffer_head bh;
> +	unsigned seg;
> +	ssize_t retval = -EINVAL;
> +	loff_t end = offset;
> +
> +	for (seg = 0; seg < nr_segs; seg++)
> +		end += iov[seg].iov_len;
> +
> +	if ((flags & DIO_LOCKING) && (rw == READ)) {
> +		struct address_space *mapping = inode->i_mapping;
> +		mutex_lock(&inode->i_mutex);
> +		retval = filemap_write_and_wait_range(mapping, offset, end - 1);
> +		if (retval) {
> +			mutex_unlock(&inode->i_mutex);
> +			goto out;
> +		}
> +	}
> +
> +	/* Protects against truncate */
> +	atomic_inc(&inode->i_dio_count);
> +
> +	retval = xip_io(rw, inode, iov, offset, end, nr_segs, get_block, &bh);
> +
> +	if ((flags & DIO_LOCKING) && (rw == READ))
> +		mutex_unlock(&inode->i_mutex);
> +
> +	inode_dio_done(inode);
> +
> +	if ((retval > 0) && end_io)
> +		end_io(iocb, offset, retval, bh.b_private);
> + out:
> +	return retval;
> +}
> +EXPORT_SYMBOL_GPL(xip_do_io);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 80cfb42..7cc5bf7 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2509,17 +2509,22 @@ extern int generic_file_open(struct inode * inode, struct file * filp);
>  extern int nonseekable_open(struct inode * inode, struct file * filp);
>  
>  #ifdef CONFIG_FS_XIP
> -extern ssize_t xip_file_read(struct file *filp, char __user *buf, size_t len,
> -			     loff_t *ppos);
>  extern int xip_file_mmap(struct file * file, struct vm_area_struct * vma);
> -extern ssize_t xip_file_write(struct file *filp, const char __user *buf,
> -			      size_t len, loff_t *ppos);
>  extern int xip_truncate_page(struct address_space *mapping, loff_t from);
> +ssize_t xip_do_io(int rw, struct kiocb *, struct inode *, const struct iovec *,
> +		loff_t, unsigned segs, get_block_t, dio_iodone_t, int flags);
>  #else
>  static inline int xip_truncate_page(struct address_space *mapping, loff_t from)
>  {
>  	return 0;
>  }
> +
> +static inline ssize_t xip_do_io(int rw, struct kiocb *iocb, struct inode *inode,
> +		const struct iovec *iov, loff_t offset, unsigned nr_segs,
> +		get_block_t get_block, dio_iodone_t end_io, int flags)
> +{
> +	return -ENOTTY;
> +}
>  #endif
>  
>  #ifdef CONFIG_BLOCK
> @@ -2669,6 +2674,11 @@ extern int generic_show_options(struct seq_file *m, struct dentry *root);
>  extern void save_mount_options(struct super_block *sb, char *options);
>  extern void replace_mount_options(struct super_block *sb, char *options);
>  
> +static inline bool io_is_direct(struct file *filp)
> +{
> +	return (filp->f_flags & O_DIRECT) || IS_XIP(file_inode(filp));
> +}
> +
>  static inline ino_t parent_ino(struct dentry *dentry)
>  {
>  	ino_t res;
> diff --git a/mm/filemap.c b/mm/filemap.c
> index b7749a9..61a31f0 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1417,8 +1417,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>  	if (retval)
>  		return retval;
>  
> -	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
> -	if (filp->f_flags & O_DIRECT) {
> +	if (io_is_direct(filp)) {
>  		loff_t size;
>  		struct address_space *mapping;
>  		struct inode *inode;
> @@ -2470,8 +2469,7 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>  	if (err)
>  		goto out;
>  
> -	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
> -	if (unlikely(file->f_flags & O_DIRECT)) {
> +	if (io_is_direct(file)) {
>  		loff_t endbyte;
>  		ssize_t written_buffered;
>  
> diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
> index c8d23e9..f7c37a1 100644
> --- a/mm/filemap_xip.c
> +++ b/mm/filemap_xip.c
> @@ -42,119 +42,6 @@ static struct page *xip_sparse_page(void)
>  }
>  
>  /*
> - * This is a file read routine for execute in place files, and uses
> - * the mapping->a_ops->get_xip_mem() function for the actual low-level
> - * stuff.
> - *
> - * Note the struct file* is not used at all.  It may be NULL.
> - */
> -static ssize_t
> -do_xip_mapping_read(struct address_space *mapping,
> -		    struct file_ra_state *_ra,
> -		    struct file *filp,
> -		    char __user *buf,
> -		    size_t len,
> -		    loff_t *ppos)
> -{
> -	struct inode *inode = mapping->host;
> -	pgoff_t index, end_index;
> -	unsigned long offset;
> -	loff_t isize, pos;
> -	size_t copied = 0, error = 0;
> -
> -	BUG_ON(!mapping->a_ops->get_xip_mem);
> -
> -	pos = *ppos;
> -	index = pos >> PAGE_CACHE_SHIFT;
> -	offset = pos & ~PAGE_CACHE_MASK;
> -
> -	isize = i_size_read(inode);
> -	if (!isize)
> -		goto out;
> -
> -	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
> -	do {
> -		unsigned long nr, left;
> -		void *xip_mem;
> -		unsigned long xip_pfn;
> -		int zero = 0;
> -
> -		/* nr is the maximum number of bytes to copy from this page */
> -		nr = PAGE_CACHE_SIZE;
> -		if (index >= end_index) {
> -			if (index > end_index)
> -				goto out;
> -			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
> -			if (nr <= offset) {
> -				goto out;
> -			}
> -		}
> -		nr = nr - offset;
> -		if (nr > len - copied)
> -			nr = len - copied;
> -
> -		error = mapping->a_ops->get_xip_mem(mapping, index, 0,
> -							&xip_mem, &xip_pfn);
> -		if (unlikely(error)) {
> -			if (error == -ENODATA) {
> -				/* sparse */
> -				zero = 1;
> -			} else
> -				goto out;
> -		}
> -
> -		/* If users can be writing to this page using arbitrary
> -		 * virtual addresses, take care about potential aliasing
> -		 * before reading the page on the kernel side.
> -		 */
> -		if (mapping_writably_mapped(mapping))
> -			/* address based flush */ ;
> -
> -		/*
> -		 * Ok, we have the mem, so now we can copy it to user space...
> -		 *
> -		 * The actor routine returns how many bytes were actually used..
> -		 * NOTE! This may not be the same as how much of a user buffer
> -		 * we filled up (we may be padding etc), so we can only update
> -		 * "pos" here (the actor routine has to update the user buffer
> -		 * pointers and the remaining count).
> -		 */
> -		if (!zero)
> -			left = __copy_to_user(buf+copied, xip_mem+offset, nr);
> -		else
> -			left = __clear_user(buf + copied, nr);
> -
> -		if (left) {
> -			error = -EFAULT;
> -			goto out;
> -		}
> -
> -		copied += (nr - left);
> -		offset += (nr - left);
> -		index += offset >> PAGE_CACHE_SHIFT;
> -		offset &= ~PAGE_CACHE_MASK;
> -	} while (copied < len);
> -
> -out:
> -	*ppos = pos + copied;
> -	if (filp)
> -		file_accessed(filp);
> -
> -	return (copied ? copied : error);
> -}
> -
> -ssize_t
> -xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
> -{
> -	if (!access_ok(VERIFY_WRITE, buf, len))
> -		return -EFAULT;
> -
> -	return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
> -			    buf, len, ppos);
> -}
> -EXPORT_SYMBOL_GPL(xip_file_read);
> -
> -/*
>   * __xip_unmap is invoked from xip_unmap and
>   * xip_write
>   *
> @@ -340,127 +227,6 @@ int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
>  }
>  EXPORT_SYMBOL_GPL(xip_file_mmap);
>  
> -static ssize_t
> -__xip_file_write(struct file *filp, const char __user *buf,
> -		  size_t count, loff_t pos, loff_t *ppos)
> -{
> -	struct address_space * mapping = filp->f_mapping;
> -	const struct address_space_operations *a_ops = mapping->a_ops;
> -	struct inode 	*inode = mapping->host;
> -	long		status = 0;
> -	size_t		bytes;
> -	ssize_t		written = 0;
> -
> -	BUG_ON(!mapping->a_ops->get_xip_mem);
> -
> -	do {
> -		unsigned long index;
> -		unsigned long offset;
> -		size_t copied;
> -		void *xip_mem;
> -		unsigned long xip_pfn;
> -
> -		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
> -		index = pos >> PAGE_CACHE_SHIFT;
> -		bytes = PAGE_CACHE_SIZE - offset;
> -		if (bytes > count)
> -			bytes = count;
> -
> -		status = a_ops->get_xip_mem(mapping, index, 0,
> -						&xip_mem, &xip_pfn);
> -		if (status == -ENODATA) {
> -			/* we allocate a new page unmap it */
> -			mutex_lock(&xip_sparse_mutex);
> -			status = a_ops->get_xip_mem(mapping, index, 1,
> -							&xip_mem, &xip_pfn);
> -			mutex_unlock(&xip_sparse_mutex);
> -			if (!status)
> -				/* unmap page at pgoff from all other vmas */
> -				__xip_unmap(mapping, index);
> -		}
> -
> -		if (status)
> -			break;
> -
> -		copied = bytes -
> -			__copy_from_user_nocache(xip_mem + offset, buf, bytes);
> -
> -		if (likely(copied > 0)) {
> -			status = copied;
> -
> -			if (status >= 0) {
> -				written += status;
> -				count -= status;
> -				pos += status;
> -				buf += status;
> -			}
> -		}
> -		if (unlikely(copied != bytes))
> -			if (status >= 0)
> -				status = -EFAULT;
> -		if (status < 0)
> -			break;
> -	} while (count);
> -	*ppos = pos;
> -	/*
> -	 * No need to use i_size_read() here, the i_size
> -	 * cannot change under us because we hold i_mutex.
> -	 */
> -	if (pos > inode->i_size) {
> -		i_size_write(inode, pos);
> -		mark_inode_dirty(inode);
> -	}
> -
> -	return written ? written : status;
> -}
> -
> -ssize_t
> -xip_file_write(struct file *filp, const char __user *buf, size_t len,
> -	       loff_t *ppos)
> -{
> -	struct address_space *mapping = filp->f_mapping;
> -	struct inode *inode = mapping->host;
> -	size_t count;
> -	loff_t pos;
> -	ssize_t ret;
> -
> -	mutex_lock(&inode->i_mutex);
> -
> -	if (!access_ok(VERIFY_READ, buf, len)) {
> -		ret=-EFAULT;
> -		goto out_up;
> -	}
> -
> -	pos = *ppos;
> -	count = len;
> -
> -	/* We can write back this queue in page reclaim */
> -	current->backing_dev_info = mapping->backing_dev_info;
> -
> -	ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
> -	if (ret)
> -		goto out_backing;
> -	if (count == 0)
> -		goto out_backing;
> -
> -	ret = file_remove_suid(filp);
> -	if (ret)
> -		goto out_backing;
> -
> -	ret = file_update_time(filp);
> -	if (ret)
> -		goto out_backing;
> -
> -	ret = __xip_file_write (filp, buf, count, pos, ppos);
> -
> - out_backing:
> -	current->backing_dev_info = NULL;
> - out_up:
> -	mutex_unlock(&inode->i_mutex);
> -	return ret;
> -}
> -EXPORT_SYMBOL_GPL(xip_file_write);
> -
>  /*
>   * truncate a page used for execute in place
>   * functionality is analog to block_truncate_page but does use get_xip_mem
> -- 
> 1.8.5.2
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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