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    /*
     * mm/fadvise.c
     *
     * Copyright (C) 2002, Linus Torvalds
     *
     * 11Jan2003	Andrew Morton
     *		Initial version.
     */
    
    #include <linux/kernel.h>
    #include <linux/file.h>
    #include <linux/fs.h>
    #include <linux/mm.h>
    #include <linux/pagemap.h>
    #include <linux/backing-dev.h>
    #include <linux/pagevec.h>
    #include <linux/fadvise.h>
    #include <linux/writeback.h>
    #include <linux/syscalls.h>
    #include <linux/swap.h>
    
    #include <asm/unistd.h>
    
    /*
     * POSIX_FADV_WILLNEED could set PG_Referenced, and POSIX_FADV_NOREUSE could
     * deactivate the pages and clear PG_Referenced.
     */
    SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
    {
    	struct fd f = fdget(fd);
    	struct inode *inode;
    	struct address_space *mapping;
    	struct backing_dev_info *bdi;
    	loff_t endbyte;			/* inclusive */
    	pgoff_t start_index;
    	pgoff_t end_index;
    	unsigned long nrpages;
    	int ret = 0;
    
    	if (!f.file)
    		return -EBADF;
    
    	inode = file_inode(f.file);
    	if (S_ISFIFO(inode->i_mode)) {
    		ret = -ESPIPE;
    		goto out;
    	}
    
    	mapping = f.file->f_mapping;
    	if (!mapping || len < 0) {
    		ret = -EINVAL;
    		goto out;
    	}
    
    	if (IS_DAX(inode)) {
    		switch (advice) {
    		case POSIX_FADV_NORMAL:
    		case POSIX_FADV_RANDOM:
    		case POSIX_FADV_SEQUENTIAL:
    		case POSIX_FADV_WILLNEED:
    		case POSIX_FADV_NOREUSE:
    		case POSIX_FADV_DONTNEED:
    			/* no bad return value, but ignore advice */
    			break;
    		default:
    			ret = -EINVAL;
    		}
    		goto out;
    	}
    
    	/* Careful about overflows. Len == 0 means "as much as possible" */
    	endbyte = offset + len;
    	if (!len || endbyte < len)
    		endbyte = -1;
    	else
    		endbyte--;		/* inclusive */
    
    	bdi = inode_to_bdi(mapping->host);
    
    	switch (advice) {
    	case POSIX_FADV_NORMAL:
    		f.file->f_ra.ra_pages = bdi->ra_pages;
    		spin_lock(&f.file->f_lock);
    		f.file->f_mode &= ~FMODE_RANDOM;
    		spin_unlock(&f.file->f_lock);
    		break;
    	case POSIX_FADV_RANDOM:
    		spin_lock(&f.file->f_lock);
    		f.file->f_mode |= FMODE_RANDOM;
    		spin_unlock(&f.file->f_lock);
    		break;
    	case POSIX_FADV_SEQUENTIAL:
    		f.file->f_ra.ra_pages = bdi->ra_pages * 2;
    		spin_lock(&f.file->f_lock);
    		f.file->f_mode &= ~FMODE_RANDOM;
    		spin_unlock(&f.file->f_lock);
    		break;
    	case POSIX_FADV_WILLNEED:
    		/* First and last PARTIAL page! */
    		start_index = offset >> PAGE_SHIFT;
    		end_index = endbyte >> PAGE_SHIFT;
    
    		/* Careful about overflow on the "+1" */
    		nrpages = end_index - start_index + 1;
    		if (!nrpages)
    			nrpages = ~0UL;
    
    		/*
    		 * Ignore return value because fadvise() shall return
    		 * success even if filesystem can't retrieve a hint,
    		 */
    		force_page_cache_readahead(mapping, f.file, start_index,
    					   nrpages);
    		break;
    	case POSIX_FADV_NOREUSE:
    		break;
    	case POSIX_FADV_DONTNEED:
    		if (!inode_write_congested(mapping->host))
    			__filemap_fdatawrite_range(mapping, offset, endbyte,
    						   WB_SYNC_NONE);
    
    		/*
    		 * First and last FULL page! Partial pages are deliberately
    		 * preserved on the expectation that it is better to preserve
    		 * needed memory than to discard unneeded memory.
    		 */
    		start_index = (offset+(PAGE_SIZE-1)) >> PAGE_SHIFT;
    		end_index = (endbyte >> PAGE_SHIFT);
    		if ((endbyte & ~PAGE_MASK) != ~PAGE_MASK) {
    			/* First page is tricky as 0 - 1 = -1, but pgoff_t
    			 * is unsigned, so the end_index >= start_index
    			 * check below would be true and we'll discard the whole
    			 * file cache which is not what was asked.
    			 */
    			if (end_index == 0)
    				break;
    
    			end_index--;
    		}
    
    		if (end_index >= start_index) {
    			unsigned long count = invalidate_mapping_pages(mapping,
    						start_index, end_index);
    
    			/*
    			 * If fewer pages were invalidated than expected then
    			 * it is possible that some of the pages were on
    			 * a per-cpu pagevec for a remote CPU. Drain all
    			 * pagevecs and try again.
    			 */
    			if (count < (end_index - start_index + 1)) {
    				lru_add_drain_all();
    				invalidate_mapping_pages(mapping, start_index,
    						end_index);
    			}
    		}
    		break;
    	default:
    		ret = -EINVAL;
    	}
    out:
    	fdput(f);
    	return ret;
    }
    
    #ifdef __ARCH_WANT_SYS_FADVISE64
    
    SYSCALL_DEFINE4(fadvise64, int, fd, loff_t, offset, size_t, len, int, advice)
    {
    	return sys_fadvise64_64(fd, offset, len, advice);
    }
    
    #endif