This provides generic support for MADV_WILLWRITE. It creates and maps buffer heads, but it should not result in anything being marked dirty.
Signed-off-by: Andy Lutomirski <[email protected]> --- As described in the 0/0 summary, this may have issues. fs/buffer.c | 57 +++++++++++++++++++++++++++++++++++++++++++++ include/linux/buffer_head.h | 3 +++ 2 files changed, 60 insertions(+) diff --git a/fs/buffer.c b/fs/buffer.c index 4d74335..017e822 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2444,6 +2444,63 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf, } EXPORT_SYMBOL(block_page_mkwrite); +long block_willwrite(struct vm_area_struct *vma, + unsigned long start, unsigned long end, + get_block_t get_block) +{ + long ret = 0; + loff_t size; + struct inode *inode = file_inode(vma->vm_file); + struct super_block *sb = inode->i_sb; + + for (; start < end; start += PAGE_CACHE_SIZE) { + struct page *p; + int size_in_page; + int tmp = get_user_pages_fast(start, 1, 0, &p); + if (tmp == 0) + tmp = -EFAULT; + if (tmp != 1) { + ret = tmp; + break; + } + + sb_start_pagefault(sb); + + lock_page(p); + size = i_size_read(inode); + if (WARN_ON_ONCE(p->mapping != inode->i_mapping) || + (page_offset(p) > size)) { + ret = -EFAULT; /* A real write would have failed. */ + goto pagedone_unlock; + } + + /* page is partially inside EOF? */ + if (((p->index + 1) << PAGE_CACHE_SHIFT) > size) + size_in_page = size & ~PAGE_CACHE_MASK; + else + size_in_page = PAGE_CACHE_SIZE; + + tmp = __block_write_begin(p, 0, size_in_page, get_block); + if (tmp) { + ret = tmp; + goto pagedone_unlock; + } + + ret += PAGE_CACHE_SIZE; + + /* No need to commit -- we're not writing anything yet. */ + + pagedone_unlock: + unlock_page(p); + sb_end_pagefault(sb); + if (ret < 0) + break; + } + + return ret; +} +EXPORT_SYMBOL(block_willwrite); + /* * nobh_write_begin()'s prereads are special: the buffer_heads are freed * immediately, while under the page lock. So it needs a special end_io diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 91fa9a9..c84639d 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -230,6 +230,9 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf, get_block_t get_block); int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf, get_block_t get_block); +long block_willwrite(struct vm_area_struct *vma, + unsigned long start, unsigned long end, + get_block_t get_block); /* Convert errno to return value from ->page_mkwrite() call */ static inline int block_page_mkwrite_return(int err) { -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
