Merge tag 'v3.10.92' into update

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / drivers / char / mem.c

/*
 *  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/crash_dump.h>
#include <linux/backing-dev.h>
#include <linux/bootmem.h>
#include <linux/splice.h>
#include <linux/pfn.h>
#include <linux/export.h>
#include <linux/io.h>
#include <linux/aio.h>

#include <asm/uaccess.h>

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

#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

#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM)
#ifdef CONFIG_STRICT_DEVMEM
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)) {
                        printk(KERN_INFO
                "Program %s tried to access /dev/mem between %Lx->%Lx.\n",
                                current->comm, from, to);
                        return 0;
                }
                cursor += PAGE_SIZE;
                pfn++;
        }
        return 1;
}
#else
static inline int range_is_allowed(unsigned long pfn, unsigned long size)
{
        return 1;
}
#endif
#endif

#ifdef CONFIG_DEVMEM
void __weak unxlate_dev_mem_ptr(unsigned long phys, void *addr)
{
}

/*
 * 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;
        char *ptr;

        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

        while (count > 0) {
                unsigned long remaining;

                sz = size_inside_page(p, count);

                if (!range_is_allowed(p >> PAGE_SHIFT, count))
                        return -EPERM;

                /*
                 * 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)
                        return -EFAULT;

                remaining = copy_to_user(buf, ptr, sz);
                unxlate_dev_mem_ptr(p, ptr);
                if (remaining)
                        return -EFAULT;

                buf += sz;
                p += sz;
                count -= sz;
                read += sz;
        }

        *ppos += read;
        return read;
}

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 (!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) {
                sz = size_inside_page(p, count);

                if (!range_is_allowed(p >> PAGE_SHIFT, sz))
                        return -EPERM;

                /*
                 * 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;
        }

        *ppos += written;
        return written;
}
#endif  /* CONFIG_DEVMEM */

#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM)

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;
}

/* 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
#define get_unmapped_area_mem   NULL

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;

        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;
}
#endif  /* CONFIG_DEVMEM */

#ifdef CONFIG_DEVKMEM
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);
}
#endif

#ifdef CONFIG_CRASH_DUMP
/*
 * Read memory corresponding to the old kernel.
 */
static ssize_t read_oldmem(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
{
        unsigned long pfn, offset;
        size_t read = 0, csize;
        int rc = 0;

        while (count) {
                pfn = *ppos / PAGE_SIZE;
                if (pfn > saved_max_pfn)
                        return read;

                offset = (unsigned long)(*ppos % PAGE_SIZE);
                if (count > PAGE_SIZE - offset)
                        csize = PAGE_SIZE - offset;
                else
                        csize = count;

                rc = copy_oldmem_page(pfn, buf, csize, offset, 1);
                if (rc < 0)
                        return rc;
                buf += csize;
                *ppos += csize;
                read += csize;
                count -= csize;
        }
        return read;
}
#endif

#ifdef CONFIG_DEVKMEM
/*
 * 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((char *)p);

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

        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;
                }
                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) {
                char *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((char *)p);

                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;
        }

        *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;
                }
                free_page((unsigned long)kbuf);
        }

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

#ifdef CONFIG_DEVPORT
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(VERIFY_WRITE, 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(VERIFY_READ, 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;
}
#endif

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 aio_read_null(struct kiocb *iocb, const struct iovec *iov,
                             unsigned long nr_segs, loff_t pos)
{
        return 0;
}

static ssize_t aio_write_null(struct kiocb *iocb, const struct iovec *iov,
                              unsigned long nr_segs, loff_t pos)
{
        return iov_length(iov, nr_segs);
}

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_zero(struct file *file, char __user *buf,
                         size_t count, loff_t *ppos)
{
        size_t written;

        if (!count)
                return 0;

        if (!access_ok(VERIFY_WRITE, buf, count))
                return -EFAULT;

        written = 0;
        while (count) {
                unsigned long unwritten;
                size_t chunk = count;

                if (chunk > PAGE_SIZE)
                        chunk = PAGE_SIZE;      /* Just for latency reasons */
                unwritten = __clear_user(buf, chunk);
                written += chunk - unwritten;
                if (unwritten)
                        break;
                if (signal_pending(current))
                        return written ? written : -ERESTARTSYS;
                buf += chunk;
                count -= chunk;
                cond_resched();
        }
        return written ? written : -EFAULT;
}

static ssize_t aio_read_zero(struct kiocb *iocb, const struct iovec *iov,
                             unsigned long nr_segs, loff_t pos)
{
        size_t written = 0;
        unsigned long i;
        ssize_t ret;

        for (i = 0; i < nr_segs; i++) {
                ret = read_zero(iocb->ki_filp, iov[i].iov_base, iov[i].iov_len,
                                &pos);
                if (ret < 0)
                        break;
                written += ret;
        }

        return written ? written : -EFAULT;
}

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);
        return 0;
}

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;
}

#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM) || defined(CONFIG_DEVPORT)

/*
 * 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;

        mutex_lock(&file_inode(file)->i_mutex);
        switch (orig) {
        case SEEK_CUR:
                offset += file->f_pos;
        case SEEK_SET:
                /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
                if ((unsigned long long)offset >= ~0xFFFULL) {
                        ret = -EOVERFLOW;
                        break;
                }
                file->f_pos = offset;
                ret = file->f_pos;
                force_successful_syscall_return();
                break;
        default:
                ret = -EINVAL;
        }
        mutex_unlock(&file_inode(file)->i_mutex);
        return ret;
}

#endif

#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM) || defined(CONFIG_DEVPORT)
static int open_port(struct inode *inode, struct file *filp)
{
        return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
}
#endif

#define zero_lseek      null_lseek
#define full_lseek      null_lseek
#define write_zero      write_null
#define read_full       read_zero
#define aio_write_zero  aio_write_null
#define open_mem        open_port
#define open_kmem       open_mem
#define open_oldmem     open_mem

#ifdef CONFIG_DEVMEM
static const struct file_operations mem_fops = {
        .llseek         = memory_lseek,
        .read           = read_mem,
        .write          = write_mem,
        .mmap           = mmap_mem,
        .open           = open_mem,
        .get_unmapped_area = get_unmapped_area_mem,
};
#endif

#ifdef CONFIG_DEVKMEM
static const struct file_operations kmem_fops = {
        .llseek         = memory_lseek,
        .read           = read_kmem,
        .write          = write_kmem,
        .mmap           = mmap_kmem,
        .open           = open_kmem,
        .get_unmapped_area = get_unmapped_area_mem,
};
#endif

static const struct file_operations null_fops = {
        .llseek         = null_lseek,
        .read           = read_null,
        .write          = write_null,
        .aio_read       = aio_read_null,
        .aio_write      = aio_write_null,
        .splice_write   = splice_write_null,
};

#ifdef CONFIG_DEVPORT
static const struct file_operations port_fops = {
        .llseek         = memory_lseek,
        .read           = read_port,
        .write          = write_port,
        .open           = open_port,
};
#endif

static const struct file_operations zero_fops = {
        .llseek         = zero_lseek,
        .read           = read_zero,
        .write          = write_zero,
        .aio_read       = aio_read_zero,
        .aio_write      = aio_write_zero,
        .mmap           = mmap_zero,
};

/*
 * capabilities for /dev/zero
 * - permits private mappings, "copies" are taken of the source of zeros
 * - no writeback happens
 */
static struct backing_dev_info zero_bdi = {
        .name           = "char/mem",
        .capabilities   = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
};

static const struct file_operations full_fops = {
        .llseek         = full_lseek,
        .read           = read_full,
        .write          = write_full,
};

#ifdef CONFIG_CRASH_DUMP
static const struct file_operations oldmem_fops = {
        .read   = read_oldmem,
        .open   = open_oldmem,
        .llseek = default_llseek,
};
#endif

static const struct memdev {
        const char *name;
        umode_t mode;
        const struct file_operations *fops;
        struct backing_dev_info *dev_info;
} devlist[] = {
#ifdef CONFIG_DEVMEM
         [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },
#endif
#ifdef CONFIG_DEVKMEM
         [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
#endif
         [3] = { "null", 0666, &null_fops, NULL },
#ifdef CONFIG_DEVPORT
         [4] = { "port", 0, &port_fops, NULL },
#endif
         [5] = { "zero", 0666, &zero_fops, &zero_bdi },
         [7] = { "full", 0666, &full_fops, NULL },
         [8] = { "random", 0666, &random_fops, NULL },
         [9] = { "urandom", 0666, &urandom_fops, NULL },
#ifdef CONFIG_PRINTK
        [11] = { "kmsg", 0644, &kmsg_fops, NULL },
#endif
#ifdef CONFIG_CRASH_DUMP
        [12] = { "oldmem", 0, &oldmem_fops, NULL },
#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;
        if (dev->dev_info)
                filp->f_mapping->backing_dev_info = dev->dev_info;

        /* Is /dev/mem or /dev/kmem ? */
        if (dev->dev_info == &directly_mappable_cdev_bdi)
                filp->f_mode |= FMODE_UNSIGNED_OFFSET;

        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 __init chr_dev_init(void)
{
        int minor;
        int err;

        err = bdi_init(&zero_bdi);
        if (err)
                return err;

        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;

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

        return tty_init();
}

fs_initcall(chr_dev_init);