// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/drivers/char/mem.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added devfs support.
 *    Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
 *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
 */

#include <linux/mm.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mman.h>
#include <linux/random.h>
#include <linux/init.h>
#include <linux/raw.h>
#include <linux/tty.h>
#include <linux/capability.h>
#include <linux/ptrace.h>
#include <linux/device.h>
#include <linux/highmem.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/splice.h>
#include <linux/pfn.h>
#include <linux/export.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/uaccess.h>
#include <linux/security.h>
#include <linux/pseudo_fs.h>
#include <uapi/linux/magic.h>
#include <linux/mount.h>

#ifdef CONFIG_IA64
# include <linux/efi.h>
#endif

#define DEVMEM_MINOR    1
#define DEVPORT_MINOR   4

static inline unsigned long size_inside_page(unsigned long start,
                                             unsigned long size)
{
        unsigned long sz;

        sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));

        return min(sz, size);
}

#ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE
static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
{
        return addr + count <= __pa(high_memory);
}

static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
{
        return 1;
}
#endif

#ifdef CONFIG_STRICT_DEVMEM
static inline int page_is_allowed(unsigned long pfn)
{
        return devmem_is_allowed(pfn);
}
static inline int range_is_allowed(unsigned long pfn, unsigned long size)
{
        u64 from = ((u64)pfn) << PAGE_SHIFT;
        u64 to = from + size;
        u64 cursor = from;

        while (cursor < to) {
                if (!devmem_is_allowed(pfn))
                        return 0;
                cursor += PAGE_SIZE;
                pfn++;
        }
        return 1;
}
#else
static inline int page_is_allowed(unsigned long pfn)
{
        return 1;
}
static inline int range_is_allowed(unsigned long pfn, unsigned long size)
{
        return 1;
}
#endif

#ifndef unxlate_dev_mem_ptr
#define unxlate_dev_mem_ptr unxlate_dev_mem_ptr
void __weak unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
{
}
#endif

static inline bool should_stop_iteration(void)
{
        if (need_resched())
                cond_resched();
        return fatal_signal_pending(current);
}

/*
 * This funcion reads the *physical* memory. The f_pos points directly to the
 * memory location.
 */
static ssize_t read_mem(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        phys_addr_t p = *ppos;
        ssize_t read, sz;
        void *ptr;
        char *bounce;
        int err;

        if (p != *ppos)
                return 0;

        if (!valid_phys_addr_range(p, count))
                return -EFAULT;
        read = 0;
#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
        /* we don't have page 0 mapped on sparc and m68k.. */
        if (p < PAGE_SIZE) {
                sz = size_inside_page(p, count);
                if (sz > 0) {
                        if (clear_user(buf, sz))
                                return -EFAULT;
                        buf += sz;
                        p += sz;
                        count -= sz;
                        read += sz;
                }
        }
#endif

        bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!bounce)
                return -ENOMEM;

        while (count > 0) {
                unsigned long remaining;
                int allowed, probe;

                sz = size_inside_page(p, count);

                err = -EPERM;
                allowed = page_is_allowed(p >> PAGE_SHIFT);
                if (!allowed)
                        goto failed;

                err = -EFAULT;
                if (allowed == 2) {
                        /* Show zeros for restricted memory. */
                        remaining = clear_user(buf, sz);
                } else {
                        /*
                         * On ia64 if a page has been mapped somewhere as
                         * uncached, then it must also be accessed uncached
                         * by the kernel or data corruption may occur.
                         */
                        ptr = xlate_dev_mem_ptr(p);
                        if (!ptr)
                                goto failed;

                        probe = copy_from_kernel_nofault(bounce, ptr, sz);
                        unxlate_dev_mem_ptr(p, ptr);
                        if (probe)
                                goto failed;

                        remaining = copy_to_user(buf, bounce, sz);
                }

                if (remaining)
                        goto failed;

                buf += sz;
                p += sz;
                count -= sz;
                read += sz;
                if (should_stop_iteration())
                        break;
        }
        kfree(bounce);

        *ppos += read;
        return read;

failed:
        kfree(bounce);
        return err;
}

static ssize_t write_mem(struct file *file, const char __user *buf,
                         size_t count, loff_t *ppos)
{
        phys_addr_t p = *ppos;
        ssize_t written, sz;
        unsigned long copied;
        void *ptr;

        if (p != *ppos)
                return -EFBIG;

        if (!valid_phys_addr_range(p, count))
                return -EFAULT;

        written = 0;

#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
        /* we don't have page 0 mapped on sparc and m68k.. */
        if (p < PAGE_SIZE) {
                sz = size_inside_page(p, count);
                /* Hmm. Do something? */
                buf += sz;
                p += sz;
                count -= sz;
                written += sz;
        }
#endif

        while (count > 0) {
                int allowed;

                sz = size_inside_page(p, count);

                allowed = page_is_allowed(p >> PAGE_SHIFT);
                if (!allowed)
                        return -EPERM;

                /* Skip actual writing when a page is marked as restricted. */
                if (allowed == 1) {
                        /*
                         * On ia64 if a page has been mapped somewhere as
                         * uncached, then it must also be accessed uncached
                         * by the kernel or data corruption may occur.
                         */
                        ptr = xlate_dev_mem_ptr(p);
                        if (!ptr) {
                                if (written)
                                        break;
                                return -EFAULT;
                        }

                        copied = copy_from_user(ptr, buf, sz);
                        unxlate_dev_mem_ptr(p, ptr);
                        if (copied) {
                                written += sz - copied;
                                if (written)
                                        break;
                                return -EFAULT;
                        }
                }

                buf += sz;
                p += sz;
                count -= sz;
                written += sz;
                if (should_stop_iteration())
                        break;
        }

        *ppos += written;
        return written;
}

int __weak phys_mem_access_prot_allowed(struct file *file,
        unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
{
        return 1;
}

#ifndef __HAVE_PHYS_MEM_ACCESS_PROT

/*
 * Architectures vary in how they handle caching for addresses
 * outside of main memory.
 *
 */
#ifdef pgprot_noncached
static int uncached_access(struct file *file, phys_addr_t addr)
{
#if defined(CONFIG_IA64)
        /*
         * On ia64, we ignore O_DSYNC because we cannot tolerate memory
         * attribute aliases.
         */
        return !(efi_mem_attributes(addr) & EFI_MEMORY_WB);
#elif defined(CONFIG_MIPS)
        {
                extern int __uncached_access(struct file *file,
                                             unsigned long addr);

                return __uncached_access(file, addr);
        }
#else
        /*
         * Accessing memory above the top the kernel knows about or through a
         * file pointer
         * that was marked O_DSYNC will be done non-cached.
         */
        if (file->f_flags & O_DSYNC)
                return 1;
        return addr >= __pa(high_memory);
#endif
}
#endif

static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
                                     unsigned long size, pgprot_t vma_prot)
{
#ifdef pgprot_noncached
        phys_addr_t offset = pfn << PAGE_SHIFT;

        if (uncached_access(file, offset))
                return pgprot_noncached(vma_prot);
#endif
        return vma_prot;
}
#endif

#ifndef CONFIG_MMU
static unsigned long get_unmapped_area_mem(struct file *file,
                                           unsigned long addr,
                                           unsigned long len,
                                           unsigned long pgoff,
                                           unsigned long flags)
{
        if (!valid_mmap_phys_addr_range(pgoff, len))
                return (unsigned long) -EINVAL;
        return pgoff << PAGE_SHIFT;
}

/* permit direct mmap, for read, write or exec */
static unsigned memory_mmap_capabilities(struct file *file)
{
        return NOMMU_MAP_DIRECT |
                NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
}

static unsigned zero_mmap_capabilities(struct file *file)
{
        return NOMMU_MAP_COPY;
}

/* can't do an in-place private mapping if there's no MMU */
static inline int private_mapping_ok(struct vm_area_struct *vma)
{
        return vma->vm_flags & VM_MAYSHARE;
}
#else

static inline int private_mapping_ok(struct vm_area_struct *vma)
{
        return 1;
}
#endif

static const struct vm_operations_struct mmap_mem_ops = {
#ifdef CONFIG_HAVE_IOREMAP_PROT
        .access = generic_access_phys
#endif
};

static int mmap_mem(struct file *file, struct vm_area_struct *vma)
{
        size_t size = vma->vm_end - vma->vm_start;
        phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;

        /* Does it even fit in phys_addr_t? */
        if (offset >> PAGE_SHIFT != vma->vm_pgoff)
                return -EINVAL;

        /* It's illegal to wrap around the end of the physical address space. */
        if (offset + (phys_addr_t)size - 1 < offset)
                return -EINVAL;

        if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
                return -EINVAL;

        if (!private_mapping_ok(vma))
                return -ENOSYS;

        if (!range_is_allowed(vma->vm_pgoff, size))
                return -EPERM;

        if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
                                                &vma->vm_page_prot))
                return -EINVAL;

        vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
                                                 size,
                                                 vma->vm_page_prot);

        vma->vm_ops = &mmap_mem_ops;

        /* Remap-pfn-range will mark the range VM_IO */
        if (remap_pfn_range(vma,
                            vma->vm_start,
                            vma->vm_pgoff,
                            size,
                            vma->vm_page_prot)) {
                return -EAGAIN;
        }
        return 0;
}

static int mmap_kmem(struct file *file, struct vm_area_struct *vma)
{
        unsigned long pfn;

        /* Turn a kernel-virtual address into a physical page frame */
        pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT;

        /*
         * RED-PEN: on some architectures there is more mapped memory than
         * available in mem_map which pfn_valid checks for. Perhaps should add a
         * new macro here.
         *
         * RED-PEN: vmalloc is not supported right now.
         */
        if (!pfn_valid(pfn))
                return -EIO;

        vma->vm_pgoff = pfn;
        return mmap_mem(file, vma);
}

/*
 * This function reads the *virtual* memory as seen by the kernel.
 */
static ssize_t read_kmem(struct file *file, char __user *buf,
                         size_t count, loff_t *ppos)
{
        unsigned long p = *ppos;
        ssize_t low_count, read, sz;
        char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
        int err = 0;

        read = 0;
        if (p < (unsigned long) high_memory) {
                low_count = count;
                if (count > (unsigned long)high_memory - p)
                        low_count = (unsigned long)high_memory - p;

#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
                /* we don't have page 0 mapped on sparc and m68k.. */
                if (p < PAGE_SIZE && low_count > 0) {
                        sz = size_inside_page(p, low_count);
                        if (clear_user(buf, sz))
                                return -EFAULT;
                        buf += sz;
                        p += sz;
                        read += sz;
                        low_count -= sz;
                        count -= sz;
                }
#endif
                while (low_count > 0) {
                        sz = size_inside_page(p, low_count);

                        /*
                         * On ia64 if a page has been mapped somewhere as
                         * uncached, then it must also be accessed uncached
                         * by the kernel or data corruption may occur
                         */
                        kbuf = xlate_dev_kmem_ptr((void *)p);
                        if (!virt_addr_valid(kbuf))
                                return -ENXIO;

                        if (copy_to_user(buf, kbuf, sz))
                                return -EFAULT;
                        buf += sz;
                        p += sz;
                        read += sz;
                        low_count -= sz;
                        count -= sz;
                        if (should_stop_iteration()) {
                                count = 0;
                                break;
                        }
                }
        }

        if (count > 0) {
                kbuf = (char *)__get_free_page(GFP_KERNEL);
                if (!kbuf)
                        return -ENOMEM;
                while (count > 0) {
                        sz = size_inside_page(p, count);
                        if (!is_vmalloc_or_module_addr((void *)p)) {
                                err = -ENXIO;
                                break;
                        }
                        sz = vread(kbuf, (char *)p, sz);
                        if (!sz)
                                break;
                        if (copy_to_user(buf, kbuf, sz)) {
                                err = -EFAULT;
                                break;
                        }
                        count -= sz;
                        buf += sz;
                        read += sz;
                        p += sz;
                        if (should_stop_iteration())
                                break;
                }
                free_page((unsigned long)kbuf);
        }
        *ppos = p;
        return read ? read : err;
}


static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
                                size_t count, loff_t *ppos)
{
        ssize_t written, sz;
        unsigned long copied;

        written = 0;
#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
        /* we don't have page 0 mapped on sparc and m68k.. */
        if (p < PAGE_SIZE) {
                sz = size_inside_page(p, count);
                /* Hmm. Do something? */
                buf += sz;
                p += sz;
                count -= sz;
                written += sz;
        }
#endif

        while (count > 0) {
                void *ptr;

                sz = size_inside_page(p, count);

                /*
                 * On ia64 if a page has been mapped somewhere as uncached, then
                 * it must also be accessed uncached by the kernel or data
                 * corruption may occur.
                 */
                ptr = xlate_dev_kmem_ptr((void *)p);
                if (!virt_addr_valid(ptr))
                        return -ENXIO;

                copied = copy_from_user(ptr, buf, sz);
                if (copied) {
                        written += sz - copied;
                        if (written)
                                break;
                        return -EFAULT;
                }
                buf += sz;
                p += sz;
                count -= sz;
                written += sz;
                if (should_stop_iteration())
                        break;
        }

        *ppos += written;
        return written;
}

/*
 * This function writes to the *virtual* memory as seen by the kernel.
 */
static ssize_t write_kmem(struct file *file, const char __user *buf,
                          size_t count, loff_t *ppos)
{
        unsigned long p = *ppos;
        ssize_t wrote = 0;
        ssize_t virtr = 0;
        char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
        int err = 0;

        if (p < (unsigned long) high_memory) {
                unsigned long to_write = min_t(unsigned long, count,
                                               (unsigned long)high_memory - p);
                wrote = do_write_kmem(p, buf, to_write, ppos);
                if (wrote != to_write)
                        return wrote;
                p += wrote;
                buf += wrote;
                count -= wrote;
        }

        if (count > 0) {
                kbuf = (char *)__get_free_page(GFP_KERNEL);
                if (!kbuf)
                        return wrote ? wrote : -ENOMEM;
                while (count > 0) {
                        unsigned long sz = size_inside_page(p, count);
                        unsigned long n;

                        if (!is_vmalloc_or_module_addr((void *)p)) {
                                err = -ENXIO;
                                break;
                        }
                        n = copy_from_user(kbuf, buf, sz);
                        if (n) {
                                err = -EFAULT;
                                break;
                        }
                        vwrite(kbuf, (char *)p, sz);
                        count -= sz;
                        buf += sz;
                        virtr += sz;
                        p += sz;
                        if (should_stop_iteration())
                                break;
                }
                free_page((unsigned long)kbuf);
        }

        *ppos = p;
        return virtr + wrote ? : err;
}

static ssize_t read_port(struct file *file, char __user *buf,
                         size_t count, loff_t *ppos)
{
        unsigned long i = *ppos;
        char __user *tmp = buf;

        if (!access_ok(buf, count))
                return -EFAULT;
        while (count-- > 0 && i < 65536) {
                if (__put_user(inb(i), tmp) < 0)
                        return -EFAULT;
                i++;
                tmp++;
        }
        *ppos = i;
        return tmp-buf;
}

static ssize_t write_port(struct file *file, const char __user *buf,
                          size_t count, loff_t *ppos)
{
        unsigned long i = *ppos;
        const char __user *tmp = buf;

        if (!access_ok(buf, count))
                return -EFAULT;
        while (count-- > 0 && i < 65536) {
                char c;

                if (__get_user(c, tmp)) {
                        if (tmp > buf)
                                break;
                        return -EFAULT;
                }
                outb(c, i);
                i++;
                tmp++;
        }
        *ppos = i;
        return tmp-buf;
}

static ssize_t read_null(struct file *file, char __user *buf,
                         size_t count, loff_t *ppos)
{
        return 0;
}

static ssize_t write_null(struct file *file, const char __user *buf,
                          size_t count, loff_t *ppos)
{
        return count;
}

static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
{
        return 0;
}

static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
{
        size_t count = iov_iter_count(from);
        iov_iter_advance(from, count);
        return count;
}

static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
                        struct splice_desc *sd)
{
        return sd->len;
}

static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
                                 loff_t *ppos, size_t len, unsigned int flags)
{
        return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
}

static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
{
        size_t written = 0;

        while (iov_iter_count(iter)) {
                size_t chunk = iov_iter_count(iter), n;

                if (chunk > PAGE_SIZE)
                        chunk = PAGE_SIZE;      /* Just for latency reasons */
                n = iov_iter_zero(chunk, iter);
                if (!n && iov_iter_count(iter))
                        return written ? written : -EFAULT;
                written += n;
                if (signal_pending(current))
                        return written ? written : -ERESTARTSYS;
                cond_resched();
        }
        return written;
}

static int mmap_zero(struct file *file, struct vm_area_struct *vma)
{
#ifndef CONFIG_MMU
        return -ENOSYS;
#endif
        if (vma->vm_flags & VM_SHARED)
                return shmem_zero_setup(vma);
        vma_set_anonymous(vma);
        return 0;
}

static unsigned long get_unmapped_area_zero(struct file *file,
                                unsigned long addr, unsigned long len,
                                unsigned long pgoff, unsigned long flags)
{
#ifdef CONFIG_MMU
        if (flags & MAP_SHARED) {
                /*
                 * mmap_zero() will call shmem_zero_setup() to create a file,
                 * so use shmem's get_unmapped_area in case it can be huge;
                 * and pass NULL for file as in mmap.c's get_unmapped_area(),
                 * so as not to confuse shmem with our handle on "/dev/zero".
                 */
                return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
        }

        /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
        return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
#else
        return -ENOSYS;
#endif
}

static ssize_t write_full(struct file *file, const char __user *buf,
                          size_t count, loff_t *ppos)
{
        return -ENOSPC;
}

/*
 * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
 * can fopen() both devices with "a" now.  This was previously impossible.
 * -- SRB.
 */
static loff_t null_lseek(struct file *file, loff_t offset, int orig)
{
        return file->f_pos = 0;
}

/*
 * The memory devices use the full 32/64 bits of the offset, and so we cannot
 * check against negative addresses: they are ok. The return value is weird,
 * though, in that case (0).
 *
 * also note that seeking relative to the "end of file" isn't supported:
 * it has no meaning, so it returns -EINVAL.
 */
static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
{
        loff_t ret;

        inode_lock(file_inode(file));
        switch (orig) {
        case SEEK_CUR:
                offset += file->f_pos;
                /* fall through */
        case SEEK_SET:
                /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
                if ((unsigned long long)offset >= -MAX_ERRNO) {
                        ret = -EOVERFLOW;
                        break;
                }
                file->f_pos = offset;
                ret = file->f_pos;
                force_successful_syscall_return();
                break;
        default:
                ret = -EINVAL;
        }
        inode_unlock(file_inode(file));
        return ret;
}

static struct inode *devmem_inode;

#ifdef CONFIG_IO_STRICT_DEVMEM
void revoke_devmem(struct resource *res)
{
        /* pairs with smp_store_release() in devmem_init_inode() */
        struct inode *inode = smp_load_acquire(&devmem_inode);

        /*
         * Check that the initialization has completed. Losing the race
         * is ok because it means drivers are claiming resources before
         * the fs_initcall level of init and prevent /dev/mem from
         * establishing mappings.
         */
        if (!inode)
                return;

        /*
         * The expectation is that the driver has successfully marked
         * the resource busy by this point, so devmem_is_allowed()
         * should start returning false, however for performance this
         * does not iterate the entire resource range.
         */
        if (devmem_is_allowed(PHYS_PFN(res->start)) &&
            devmem_is_allowed(PHYS_PFN(res->end))) {
                /*
                 * *cringe* iomem=relaxed says "go ahead, what's the
                 * worst that can happen?"
                 */
                return;
        }

        unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
}
#endif

static int open_port(struct inode *inode, struct file *filp)
{
        int rc;

        if (!capable(CAP_SYS_RAWIO))
                return -EPERM;

        rc = security_locked_down(LOCKDOWN_DEV_MEM);
        if (rc)
                return rc;

        if (iminor(inode) != DEVMEM_MINOR)
                return 0;

        /*
         * Use a unified address space to have a single point to manage
         * revocations when drivers want to take over a /dev/mem mapped
         * range.
         */
        inode->i_mapping = devmem_inode->i_mapping;
        filp->f_mapping = inode->i_mapping;

        return 0;
}

#define zero_lseek      null_lseek
#define full_lseek      null_lseek
#define write_zero      write_null
#define write_iter_zero write_iter_null
#define open_mem        open_port
#define open_kmem       open_mem

static const struct file_operations __maybe_unused mem_fops = {
        .llseek         = memory_lseek,
        .read           = read_mem,
        .write          = write_mem,
        .mmap           = mmap_mem,
        .open           = open_mem,
#ifndef CONFIG_MMU
        .get_unmapped_area = get_unmapped_area_mem,
        .mmap_capabilities = memory_mmap_capabilities,
#endif
};

static const struct file_operations __maybe_unused kmem_fops = {
        .llseek         = memory_lseek,
        .read           = read_kmem,
        .write          = write_kmem,
        .mmap           = mmap_kmem,
        .open           = open_kmem,
#ifndef CONFIG_MMU
        .get_unmapped_area = get_unmapped_area_mem,
        .mmap_capabilities = memory_mmap_capabilities,
#endif
};

static const struct file_operations null_fops = {
        .llseek         = null_lseek,
        .read           = read_null,
        .write          = write_null,
        .read_iter      = read_iter_null,
        .write_iter     = write_iter_null,
        .splice_write   = splice_write_null,
};

static const struct file_operations __maybe_unused port_fops = {
        .llseek         = memory_lseek,
        .read           = read_port,
        .write          = write_port,
        .open           = open_port,
};

static const struct file_operations zero_fops = {
        .llseek         = zero_lseek,
        .write          = write_zero,
        .read_iter      = read_iter_zero,
        .write_iter     = write_iter_zero,
        .mmap           = mmap_zero,
        .get_unmapped_area = get_unmapped_area_zero,
#ifndef CONFIG_MMU
        .mmap_capabilities = zero_mmap_capabilities,
#endif
};

static const struct file_operations full_fops = {
        .llseek         = full_lseek,
        .read_iter      = read_iter_zero,
        .write          = write_full,
};

static const struct memdev {
        const char *name;
        umode_t mode;
        const struct file_operations *fops;
        fmode_t fmode;
} devlist[] = {
#ifdef CONFIG_DEVMEM
         [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
#endif
#ifdef CONFIG_DEVKMEM
         [2] = { "kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET },
#endif
         [3] = { "null", 0666, &null_fops, 0 },
#ifdef CONFIG_DEVPORT
         [4] = { "port", 0, &port_fops, 0 },
#endif
         [5] = { "zero", 0666, &zero_fops, 0 },
         [7] = { "full", 0666, &full_fops, 0 },
         [8] = { "random", 0666, &random_fops, 0 },
         [9] = { "urandom", 0666, &urandom_fops, 0 },
#ifdef CONFIG_PRINTK
        [11] = { "kmsg", 0644, &kmsg_fops, 0 },
#endif
};

static int memory_open(struct inode *inode, struct file *filp)
{
        int minor;
        const struct memdev *dev;

        minor = iminor(inode);
        if (minor >= ARRAY_SIZE(devlist))
                return -ENXIO;

        dev = &devlist[minor];
        if (!dev->fops)
                return -ENXIO;

        filp->f_op = dev->fops;
        filp->f_mode |= dev->fmode;

        if (dev->fops->open)
                return dev->fops->open(inode, filp);

        return 0;
}

static const struct file_operations memory_fops = {
        .open = memory_open,
        .llseek = noop_llseek,
};

static char *mem_devnode(struct device *dev, umode_t *mode)
{
        if (mode && devlist[MINOR(dev->devt)].mode)
                *mode = devlist[MINOR(dev->devt)].mode;
        return NULL;
}

static struct class *mem_class;

static int devmem_fs_init_fs_context(struct fs_context *fc)
{

        return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
}

static struct file_system_type devmem_fs_type = {
        .name           = "devmem",
        .owner          = THIS_MODULE,
        .init_fs_context = devmem_fs_init_fs_context,
        .kill_sb        = kill_anon_super,
};

static int devmem_init_inode(void)
{
        static struct vfsmount *devmem_vfs_mount;
        static int devmem_fs_cnt;
        struct inode *inode;
        int rc;

        rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt);
        if (rc < 0) {
                pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc);
                return rc;
        }

        inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb);
        if (IS_ERR(inode)) {
                rc = PTR_ERR(inode);
                pr_err("Cannot allocate inode for /dev/mem: %d\n", rc);
                simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt);
                return rc;
        }

        /*
         * Publish /dev/mem initialized.
         * Pairs with smp_load_acquire() in revoke_devmem().
         */
        smp_store_release(&devmem_inode, inode);

        return 0;
}

static int __init chr_dev_init(void)
{
        int minor;

        if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
                printk("unable to get major %d for memory devs\n", MEM_MAJOR);

        mem_class = class_create(THIS_MODULE, "mem");
        if (IS_ERR(mem_class))
                return PTR_ERR(mem_class);

        mem_class->devnode = mem_devnode;
        for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
                if (!devlist[minor].name)
                        continue;

                /*
                 * Create /dev/port?
                 */
                if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
                        continue;
                if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0)
                        continue;

                device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
                              NULL, devlist[minor].name);
        }

        return tty_init();
}

fs_initcall(chr_dev_init);