// 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>

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

static 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;

                /*
                 * Ignore return value because fadvise() shall return
                 * success even if filesystem can't retrieve a hint,
                 */
                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 count;

                        /*
                         * 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();

                        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:
                return -EINVAL;
        }
        return 0;
}

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