Add infrastructure for multipage buffered writes. This is implemented using an main iterator that applies an actor function to a range that can be written. This infrastucture is used to implement a buffered write helper, one to zero file ranges and one to implement the ->page_mkwrite VM operations. All of them borrow a fair amount of code from fs/buffers. for now by using an internal version of __block_write_begin that gets passed an iomap and builds the corresponding buffer head. The file system is gets a set of paired ->iomap_begin and ->iomap_end calls which allow it to map/reserve a range and get a notification once the write code is finished with it. Based on earlier code from Dave Chinner. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Bob Peterson <rpeterso@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>tirimbino
Christoph Hellwig
9 years ago
committed by
Dave Chinner
parent
199a31c6d9
commit
ae259a9c85
@ -0,0 +1,394 @@ |
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/*
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* Copyright (C) 2010 Red Hat, Inc. |
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* Copyright (c) 2016 Christoph Hellwig. |
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* |
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* This program is free software; you can redistribute it and/or modify it |
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* under the terms and conditions of the GNU General Public License, |
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* version 2, as published by the Free Software Foundation. |
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* |
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* This program is distributed in the hope it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
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* more details. |
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*/ |
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#include <linux/module.h> |
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#include <linux/compiler.h> |
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#include <linux/fs.h> |
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#include <linux/iomap.h> |
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#include <linux/uaccess.h> |
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#include <linux/gfp.h> |
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#include <linux/mm.h> |
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#include <linux/swap.h> |
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#include <linux/pagemap.h> |
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#include <linux/file.h> |
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#include <linux/uio.h> |
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#include <linux/backing-dev.h> |
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#include <linux/buffer_head.h> |
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#include "internal.h" |
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typedef loff_t (*iomap_actor_t)(struct inode *inode, loff_t pos, loff_t len, |
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void *data, struct iomap *iomap); |
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/*
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* Execute a iomap write on a segment of the mapping that spans a |
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* contiguous range of pages that have identical block mapping state. |
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* |
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* This avoids the need to map pages individually, do individual allocations |
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* for each page and most importantly avoid the need for filesystem specific |
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* locking per page. Instead, all the operations are amortised over the entire |
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* range of pages. It is assumed that the filesystems will lock whatever |
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* resources they require in the iomap_begin call, and release them in the |
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* iomap_end call. |
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*/ |
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static loff_t |
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iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags, |
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struct iomap_ops *ops, void *data, iomap_actor_t actor) |
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{ |
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struct iomap iomap = { 0 }; |
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loff_t written = 0, ret; |
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/*
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* Need to map a range from start position for length bytes. This can |
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* span multiple pages - it is only guaranteed to return a range of a |
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* single type of pages (e.g. all into a hole, all mapped or all |
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* unwritten). Failure at this point has nothing to undo. |
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* |
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* If allocation is required for this range, reserve the space now so |
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* that the allocation is guaranteed to succeed later on. Once we copy |
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* the data into the page cache pages, then we cannot fail otherwise we |
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* expose transient stale data. If the reserve fails, we can safely |
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* back out at this point as there is nothing to undo. |
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*/ |
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ret = ops->iomap_begin(inode, pos, length, flags, &iomap); |
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if (ret) |
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return ret; |
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if (WARN_ON(iomap.offset > pos)) |
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return -EIO; |
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/*
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* Cut down the length to the one actually provided by the filesystem, |
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* as it might not be able to give us the whole size that we requested. |
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*/ |
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if (iomap.offset + iomap.length < pos + length) |
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length = iomap.offset + iomap.length - pos; |
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/*
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* Now that we have guaranteed that the space allocation will succeed. |
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* we can do the copy-in page by page without having to worry about |
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* failures exposing transient data. |
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*/ |
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written = actor(inode, pos, length, data, &iomap); |
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/*
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* Now the data has been copied, commit the range we've copied. This |
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* should not fail unless the filesystem has had a fatal error. |
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*/ |
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ret = ops->iomap_end(inode, pos, length, written > 0 ? written : 0, |
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flags, &iomap); |
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return written ? written : ret; |
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} |
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static void |
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iomap_write_failed(struct inode *inode, loff_t pos, unsigned len) |
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{ |
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loff_t i_size = i_size_read(inode); |
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/*
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* Only truncate newly allocated pages beyoned EOF, even if the |
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* write started inside the existing inode size. |
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*/ |
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if (pos + len > i_size) |
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truncate_pagecache_range(inode, max(pos, i_size), pos + len); |
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} |
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static int |
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iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags, |
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struct page **pagep, struct iomap *iomap) |
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{ |
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pgoff_t index = pos >> PAGE_SHIFT; |
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struct page *page; |
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int status = 0; |
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BUG_ON(pos + len > iomap->offset + iomap->length); |
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page = grab_cache_page_write_begin(inode->i_mapping, index, flags); |
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if (!page) |
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return -ENOMEM; |
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status = __block_write_begin_int(page, pos, len, NULL, iomap); |
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if (unlikely(status)) { |
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unlock_page(page); |
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put_page(page); |
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page = NULL; |
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iomap_write_failed(inode, pos, len); |
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} |
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*pagep = page; |
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return status; |
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} |
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static int |
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iomap_write_end(struct inode *inode, loff_t pos, unsigned len, |
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unsigned copied, struct page *page) |
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{ |
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int ret; |
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ret = generic_write_end(NULL, inode->i_mapping, pos, len, |
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copied, page, NULL); |
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if (ret < len) |
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iomap_write_failed(inode, pos, len); |
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return ret; |
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} |
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static loff_t |
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iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data, |
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struct iomap *iomap) |
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{ |
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struct iov_iter *i = data; |
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long status = 0; |
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ssize_t written = 0; |
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unsigned int flags = AOP_FLAG_NOFS; |
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/*
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* Copies from kernel address space cannot fail (NFSD is a big user). |
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*/ |
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if (!iter_is_iovec(i)) |
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flags |= AOP_FLAG_UNINTERRUPTIBLE; |
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do { |
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struct page *page; |
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unsigned long offset; /* Offset into pagecache page */ |
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unsigned long bytes; /* Bytes to write to page */ |
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size_t copied; /* Bytes copied from user */ |
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offset = (pos & (PAGE_SIZE - 1)); |
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bytes = min_t(unsigned long, PAGE_SIZE - offset, |
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iov_iter_count(i)); |
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again: |
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if (bytes > length) |
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bytes = length; |
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/*
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* Bring in the user page that we will copy from _first_. |
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* Otherwise there's a nasty deadlock on copying from the |
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* same page as we're writing to, without it being marked |
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* up-to-date. |
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* |
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* Not only is this an optimisation, but it is also required |
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* to check that the address is actually valid, when atomic |
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* usercopies are used, below. |
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*/ |
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if (unlikely(iov_iter_fault_in_readable(i, bytes))) { |
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status = -EFAULT; |
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break; |
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} |
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status = iomap_write_begin(inode, pos, bytes, flags, &page, |
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iomap); |
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if (unlikely(status)) |
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break; |
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if (mapping_writably_mapped(inode->i_mapping)) |
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flush_dcache_page(page); |
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pagefault_disable(); |
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copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes); |
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pagefault_enable(); |
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flush_dcache_page(page); |
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mark_page_accessed(page); |
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status = iomap_write_end(inode, pos, bytes, copied, page); |
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if (unlikely(status < 0)) |
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break; |
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copied = status; |
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cond_resched(); |
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iov_iter_advance(i, copied); |
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if (unlikely(copied == 0)) { |
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/*
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* If we were unable to copy any data at all, we must |
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* fall back to a single segment length write. |
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* |
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* If we didn't fallback here, we could livelock |
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* because not all segments in the iov can be copied at |
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* once without a pagefault. |
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*/ |
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bytes = min_t(unsigned long, PAGE_SIZE - offset, |
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iov_iter_single_seg_count(i)); |
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goto again; |
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} |
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pos += copied; |
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written += copied; |
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length -= copied; |
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balance_dirty_pages_ratelimited(inode->i_mapping); |
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} while (iov_iter_count(i) && length); |
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return written ? written : status; |
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} |
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ssize_t |
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iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter, |
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struct iomap_ops *ops) |
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{ |
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struct inode *inode = iocb->ki_filp->f_mapping->host; |
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loff_t pos = iocb->ki_pos, ret = 0, written = 0; |
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while (iov_iter_count(iter)) { |
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ret = iomap_apply(inode, pos, iov_iter_count(iter), |
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IOMAP_WRITE, ops, iter, iomap_write_actor); |
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if (ret <= 0) |
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break; |
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pos += ret; |
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written += ret; |
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} |
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return written ? written : ret; |
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} |
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EXPORT_SYMBOL_GPL(iomap_file_buffered_write); |
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static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset, |
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unsigned bytes, struct iomap *iomap) |
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{ |
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struct page *page; |
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int status; |
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status = iomap_write_begin(inode, pos, bytes, |
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AOP_FLAG_UNINTERRUPTIBLE | AOP_FLAG_NOFS, &page, iomap); |
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if (status) |
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return status; |
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zero_user(page, offset, bytes); |
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mark_page_accessed(page); |
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return iomap_write_end(inode, pos, bytes, bytes, page); |
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} |
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static loff_t |
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iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count, |
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void *data, struct iomap *iomap) |
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{ |
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bool *did_zero = data; |
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loff_t written = 0; |
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int status; |
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/* already zeroed? we're done. */ |
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if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN) |
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return count; |
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do { |
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unsigned offset, bytes; |
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offset = pos & (PAGE_SIZE - 1); /* Within page */ |
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bytes = min_t(unsigned, PAGE_SIZE - offset, count); |
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status = iomap_zero(inode, pos, offset, bytes, iomap); |
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if (status < 0) |
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return status; |
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pos += bytes; |
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count -= bytes; |
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written += bytes; |
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if (did_zero) |
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*did_zero = true; |
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} while (count > 0); |
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return written; |
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} |
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int |
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iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, |
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struct iomap_ops *ops) |
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{ |
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loff_t ret; |
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while (len > 0) { |
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ret = iomap_apply(inode, pos, len, IOMAP_ZERO, |
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ops, did_zero, iomap_zero_range_actor); |
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if (ret <= 0) |
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return ret; |
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pos += ret; |
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len -= ret; |
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} |
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return 0; |
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} |
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EXPORT_SYMBOL_GPL(iomap_zero_range); |
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int |
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iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero, |
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struct iomap_ops *ops) |
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{ |
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unsigned blocksize = (1 << inode->i_blkbits); |
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unsigned off = pos & (blocksize - 1); |
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/* Block boundary? Nothing to do */ |
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if (!off) |
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return 0; |
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return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops); |
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} |
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EXPORT_SYMBOL_GPL(iomap_truncate_page); |
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static loff_t |
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iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length, |
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void *data, struct iomap *iomap) |
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{ |
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struct page *page = data; |
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int ret; |
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ret = __block_write_begin_int(page, pos & ~PAGE_MASK, length, |
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NULL, iomap); |
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if (ret) |
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return ret; |
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block_commit_write(page, 0, length); |
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return length; |
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} |
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int iomap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf, |
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struct iomap_ops *ops) |
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{ |
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struct page *page = vmf->page; |
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struct inode *inode = file_inode(vma->vm_file); |
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unsigned long length; |
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loff_t offset, size; |
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ssize_t ret; |
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lock_page(page); |
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size = i_size_read(inode); |
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if ((page->mapping != inode->i_mapping) || |
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(page_offset(page) > size)) { |
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/* We overload EFAULT to mean page got truncated */ |
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ret = -EFAULT; |
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goto out_unlock; |
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} |
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/* page is wholly or partially inside EOF */ |
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if (((page->index + 1) << PAGE_SHIFT) > size) |
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length = size & ~PAGE_MASK; |
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else |
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length = PAGE_SIZE; |
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offset = page_offset(page); |
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while (length > 0) { |
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ret = iomap_apply(inode, offset, length, IOMAP_WRITE, |
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ops, page, iomap_page_mkwrite_actor); |
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if (unlikely(ret <= 0)) |
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goto out_unlock; |
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offset += ret; |
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length -= ret; |
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} |
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set_page_dirty(page); |
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wait_for_stable_page(page); |
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return 0; |
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out_unlock: |
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unlock_page(page); |
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return ret; |
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} |
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EXPORT_SYMBOL_GPL(iomap_page_mkwrite); |
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