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Date: Thu, 29 May 2008 14:52:50 +0200
From: Jan Kara <jack@...e.cz>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: cmm@...ibm.com, tytso@....edu, sandeen@...hat.com,
linux-ext4@...r.kernel.org
Subject: Re: [Updated PATCH] ext4: Use page_mkwrite vma_operations to get
mmap write notification.
On Thu 29-05-08 17:33:45, Aneesh Kumar K.V wrote:
> We would like to get notified when we are doing a write on mmap section.
> This is needed with respect to preallocated area. We split the preallocated
> area into initialzed extent and uninitialzed extent in the call back. This
> let us handle ENOSPC better. Otherwise we get ENOSPC in the writepage and
> that would result in data loss. The changes are also needed to handle ENOSPC
> when writing to an mmap section of files with holes.
>
> Acked-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Signed-off-by: Mingming Cao <cmm@...ibm.com>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
> fs/ext4/ext4.h | 1 +
> fs/ext4/file.c | 19 +++++++++++++-
> fs/ext4/inode.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 95 insertions(+), 1 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 6605076..77cbb28 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1053,6 +1053,7 @@ extern void ext4_set_aops(struct inode *inode);
> extern int ext4_writepage_trans_blocks(struct inode *);
> extern int ext4_block_truncate_page(handle_t *handle, struct page *page,
> struct address_space *mapping, loff_t from);
> +extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
>
> /* ioctl.c */
> extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 4159be6..b9510ba 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -123,6 +123,23 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
> return ret;
> }
>
> +static struct vm_operations_struct ext4_file_vm_ops = {
> + .fault = filemap_fault,
> + .page_mkwrite = ext4_page_mkwrite,
> +};
> +
> +static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct address_space *mapping = file->f_mapping;
> +
> + if (!mapping->a_ops->readpage)
> + return -ENOEXEC;
> + file_accessed(file);
> + vma->vm_ops = &ext4_file_vm_ops;
> + vma->vm_flags |= VM_CAN_NONLINEAR;
> + return 0;
> +}
> +
> const struct file_operations ext4_file_operations = {
> .llseek = generic_file_llseek,
> .read = do_sync_read,
> @@ -133,7 +150,7 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
> #ifdef CONFIG_COMPAT
> .compat_ioctl = ext4_compat_ioctl,
> #endif
> - .mmap = generic_file_mmap,
> + .mmap = ext4_file_mmap,
> .open = generic_file_open,
> .release = ext4_release_file,
> .fsync = ext4_sync_file,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 4a7ed29..23e09eb 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3555,3 +3555,79 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>
> return err;
> }
> +
> +static int ext4_bh_prepare_fill(handle_t *handle, struct buffer_head *bh)
> +{
> + if (!buffer_mapped(bh)) {
> + /*
> + * Mark buffer as dirty so that
> + * block_write_full_page() writes it
> + */
> + set_buffer_dirty(bh);
> + }
> + return 0;
> +}
> +
> +static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
> +{
> + return !buffer_mapped(bh);
> +}
> +
> +int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +{
> + loff_t size;
> + unsigned long len;
> + int ret = -EINVAL;
> + struct file *file = vma->vm_file;
> + struct inode *inode = file->f_path.dentry->d_inode;
> + struct address_space *mapping = inode->i_mapping;
> + struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE,
> + .nr_to_write = 1 };
> +
> + /*
> + * Get i_alloc_sem to stop truncates messing with the inode. We cannot
> + * get i_mutex because we are already holding mmap_sem.
> + */
> + down_read(&inode->i_alloc_sem);
> + size = i_size_read(inode);
> + if (page->mapping != mapping || size <= page_offset(page)
> + || !PageUptodate(page)) {
> + /* page got truncated from under us? */
> + goto out_unlock;
> + }
> + ret = 0;
> + if (PageMappedToDisk(page))
> + goto out_unlock;
> +
> + if (page->index == size >> PAGE_CACHE_SHIFT)
> + len = size & ~PAGE_CACHE_MASK;
> + else
> + len = PAGE_CACHE_SIZE;
> +
> + if (page_has_buffers(page)) {
> + /* return if we have all the buffers mapped */
> + if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
> + ext4_bh_unmapped))
> + goto out_unlock;
> + /*
> + * Now mark all the buffer head dirty so
> + * that writepage can write it
> + */
> + walk_page_buffers(NULL, page_buffers(page), 0, PAGE_CACHE_SIZE,
> + NULL, ext4_bh_prepare_fill);
Just a minor nit - probably use 'len' here instead of PAGE_CACHE_SIZE.
It doesn't sound right to mark buffers dirty beyond end of file...
> + }
> + /*
> + * OK, we need to fill the hole... Lock the page and do writepage.
> + * We can't do write_begin and write_end here because we don't
> + * have inode_mutex and that allow parallel write_begin, write_end call.
> + * (lock_page prevent this from happening on the same page though)
> + */
> + lock_page(page);
> + wbc.range_start = page_offset(page);
> + wbc.range_end = page_offset(page) + len;
> + ret = mapping->a_ops->writepage(page, &wbc);
> + /* writepage unlocks the page */
> +out_unlock:
> + up_read(&inode->i_alloc_sem);
> + return ret;
> +}
> --
> 1.5.5.1.357.g1af8b.dirty
Honza
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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