// SPDX-License-Identifier: GPL-2.0

  /*
   * 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>

  #include "internal.h"

  /*
   * POSIX_FADV_WILLNEED could set PG_Referenced, and POSIX_FADV_NOREUSE could
   * deactivate the pages and clear PG_Referenced.
   */

  int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)

  {

  	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;

  	inode = file_inode(file);
  	if (S_ISFIFO(inode->i_mode))
  		return -ESPIPE;

  	mapping = file->f_mapping;
  	if (!mapping || len < 0)
  		return -EINVAL;

  	bdi = inode_to_bdi(mapping->host);
  
  	if (IS_DAX(inode) || (bdi == &noop_backing_dev_info)) {

  		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:

  			return -EINVAL;

  		}

  		return 0;

  	}

  	/*
  	 * Careful about overflows. Len == 0 means "as much as possible".  Use
  	 * unsigned math because signed overflows are undefined and UBSan
  	 * complains.
  	 */
  	endbyte = (u64)offset + (u64)len;

  	if (!len || endbyte < len)
  		endbyte = -1;

  	else
  		endbyte--;		/* inclusive */

  	switch (advice) {
  	case POSIX_FADV_NORMAL:

  		file->f_ra.ra_pages = bdi->ra_pages;
  		spin_lock(&file->f_lock);
  		file->f_mode &= ~FMODE_RANDOM;
  		spin_unlock(&file->f_lock);

  		break;
  	case POSIX_FADV_RANDOM:

  		spin_lock(&file->f_lock);
  		file->f_mode |= FMODE_RANDOM;
  		spin_unlock(&file->f_lock);

  		break;
  	case POSIX_FADV_SEQUENTIAL:

  		file->f_ra.ra_pages = bdi->ra_pages * 2;
  		spin_lock(&file->f_lock);
  		file->f_mode &= ~FMODE_RANDOM;
  		spin_unlock(&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;

  		force_page_cache_readahead(mapping, 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);

  		/*
  		 * The page at end_index will be inclusively discarded according
  		 * by invalidate_mapping_pages(), so subtracting 1 from
  		 * end_index means we will skip the last page.  But if endbyte
  		 * is page aligned or is at the end of file, we should not skip
  		 * that page - discarding the last page is safe enough.
  		 */
  		if ((endbyte & ~PAGE_MASK) != ~PAGE_MASK &&
  				endbyte != inode->i_size - 1) {

  			/* 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 nr_pagevec = 0;

  
  			/*
  			 * It's common to FADV_DONTNEED right after
  			 * the read or write that instantiates the
  			 * pages, in which case there will be some
  			 * sitting on the local LRU cache. Try to
  			 * avoid the expensive remote drain and the
  			 * second cache tree walk below by flushing
  			 * them out right away.
  			 */
  			lru_add_drain();

  			invalidate_mapping_pagevec(mapping,
  						start_index, end_index,
  						&nr_pagevec);

  
  			/*
  			 * 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 (nr_pagevec) {

  				lru_add_drain_all();
  				invalidate_mapping_pages(mapping, start_index,

  						end_index);

  			}
  		}

  		break;

  	default:

  		return -EINVAL;

  	}

  	return 0;
  }

  EXPORT_SYMBOL(generic_fadvise);

  
  int vfs_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
  {
  	if (file->f_op->fadvise)
  		return file->f_op->fadvise(file, offset, len, advice);
  
  	return generic_fadvise(file, offset, len, advice);
  }
  EXPORT_SYMBOL(vfs_fadvise);

  #ifdef CONFIG_ADVISE_SYSCALLS

  int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
  {
  	struct fd f = fdget(fd);
  	int ret;
  
  	if (!f.file)
  		return -EBADF;
  
  	ret = vfs_fadvise(f.file, offset, len, advice);

  	fdput(f);

  	return ret;
  }

  SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
  {
  	return ksys_fadvise64_64(fd, offset, len, advice);
  }

  #ifdef __ARCH_WANT_SYS_FADVISE64

  SYSCALL_DEFINE4(fadvise64, int, fd, loff_t, offset, size_t, len, int, advice)

  {

  	return ksys_fadvise64_64(fd, offset, len, advice);

  }
  
  #endif

  #endif