NOMMU: Present backing device capabilities for MTD chardevs

Present backing device capabilities for MTD character device files to allow
NOMMU mmap to do direct mapping where possible.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Bernd Schmidt <bernd.schmidt@analog.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 62 insertions, 1 deletions

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 2c8a16f49ca2..f478f1fc3949 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/smp_lock.h>
+#include <linux/backing-dev.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/compatmac.h>
@@ -107,12 +108,15 @@ static int mtd_open(struct inode *inode, struct file *file)
                 goto out;
         }
 
-        if (MTD_ABSENT == mtd->type) {
+        if (mtd->type == MTD_ABSENT) {
                 put_mtd_device(mtd);
                 ret = -ENODEV;
                 goto out;
         }
 
+        if (mtd->backing_dev_info)
+                file->f_mapping->backing_dev_info = mtd->backing_dev_info;
+
         /* You can't open it RW if it's not a writeable device */
         if ((file->f_mode & FMODE_WRITE) && !(mtd->flags & MTD_WRITEABLE)) {
                 put_mtd_device(mtd);
@@ -781,6 +785,59 @@ static int mtd_ioctl(struct inode *inode, struct file *file,
         return ret;
 } /* memory_ioctl */
 
+/*
+ * 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)
+ */
+#ifndef CONFIG_MMU
+static unsigned long mtd_get_unmapped_area(struct file *file,
+                                           unsigned long addr,
+                                           unsigned long len,
+                                           unsigned long pgoff,
+                                           unsigned long flags)
+{
+        struct mtd_file_info *mfi = file->private_data;
+        struct mtd_info *mtd = mfi->mtd;
+
+        if (mtd->get_unmapped_area) {
+                unsigned long offset;
+
+                if (addr != 0)
+                        return (unsigned long) -EINVAL;
+
+                if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
+                        return (unsigned long) -EINVAL;
+
+                offset = pgoff << PAGE_SHIFT;
+                if (offset > mtd->size - len)
+                        return (unsigned long) -EINVAL;
+
+                return mtd->get_unmapped_area(mtd, len, offset, flags);
+        }
+
+        /* can't map directly */
+        return (unsigned long) -ENOSYS;
+}
+#endif
+
+/*
+ * set up a mapping for shared memory segments
+ */
+static int mtd_mmap(struct file *file, struct vm_area_struct *vma)
+{
+#ifdef CONFIG_MMU
+        struct mtd_file_info *mfi = file->private_data;
+        struct mtd_info *mtd = mfi->mtd;
+
+        if (mtd->type == MTD_RAM || mtd->type == MTD_ROM)
+                return 0;
+        return -ENOSYS;
+#else
+        return vma->vm_flags & VM_SHARED ? 0 : -ENOSYS;
+#endif
+}
+
 static const struct file_operations mtd_fops = {
         .owner          = THIS_MODULE,
         .llseek         = mtd_lseek,
@@ -789,6 +846,10 @@ static const struct file_operations mtd_fops = {
         .ioctl          = mtd_ioctl,
         .open           = mtd_open,
         .release        = mtd_close,
+        .mmap           = mtd_mmap,
+#ifndef CONFIG_MMU
+        .get_unmapped_area = mtd_get_unmapped_area,
+#endif
 };
 
 static int __init init_mtdchar(void)