// SPDX-License-Identifier: GPL-2.0-or-later
/* NOMMU mmap support for RomFS on MTD devices
 *
 * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/mm.h>
#include <linux/mtd/super.h>
#include "internal.h"

/*
 * try to determine where a shared mapping can be made
 * - only supported for NOMMU at the moment (MMU can't doesn't copy private
 *   mappings)
 * - attempts to map through to the underlying MTD device
 */
static unsigned long romfs_get_unmapped_area(struct file *file,
                                             unsigned long addr,
                                             unsigned long len,
                                             unsigned long pgoff,
                                             unsigned long flags)
{
        struct inode *inode = file->f_mapping->host;
        struct mtd_info *mtd = inode->i_sb->s_mtd;
        unsigned long isize, offset, maxpages, lpages;
        int ret;

        if (!mtd)
                return (unsigned long) -ENOSYS;

        /* the mapping mustn't extend beyond the EOF */
        lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        isize = i_size_read(inode);
        offset = pgoff << PAGE_SHIFT;

        maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
        if ((pgoff >= maxpages) || (maxpages - pgoff < lpages))
                return (unsigned long) -EINVAL;

        if (addr != 0)
                return (unsigned long) -EINVAL;

        if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
                return (unsigned long) -EINVAL;

        offset += ROMFS_I(inode)->i_dataoffset;
        if (offset >= mtd->size)
                return (unsigned long) -EINVAL;
        /* the mapping mustn't extend beyond the EOF */
        if ((offset + len) > mtd->size)
                len = mtd->size - offset;

        ret = mtd_get_unmapped_area(mtd, len, offset, flags);
        if (ret == -EOPNOTSUPP)
                ret = -ENOSYS;
        return (unsigned long) ret;
}

/*
 * permit a R/O mapping to be made directly through onto an MTD device if
 * possible
 */
static int romfs_mmap_prepare(struct vm_area_desc *desc)
{
        return is_nommu_shared_vma_flags(&desc->vma_flags) ? 0 : -ENOSYS;
}

static unsigned romfs_mmap_capabilities(struct file *file)
{
        struct mtd_info *mtd = file_inode(file)->i_sb->s_mtd;

        if (!mtd)
                return NOMMU_MAP_COPY;
        return mtd_mmap_capabilities(mtd);
}

const struct file_operations romfs_ro_fops = {
        .llseek                 = generic_file_llseek,
        .read_iter              = generic_file_read_iter,
        .splice_read            = filemap_splice_read,
        .mmap_prepare           = romfs_mmap_prepare,
        .get_unmapped_area      = romfs_get_unmapped_area,
        .mmap_capabilities      = romfs_mmap_capabilities,
};