fs: introduce f_op->mmap_capabilities for nommu mmap support

Since "BDI: Provide backing device capability information [try #3]" the
backing_dev_info structure also provides flags for the kind of mmap
operation available in a nommu environment, which is entirely unrelated
to it's original purpose.

Introduce a new nommu-only file operation to provide this information to
the nommu mmap code instead.  Splitting this from the backing_dev_info
structure allows to remove lots of backing_dev_info instance that aren't
otherwise needed, and entirely gets rid of the concept of providing a
backing_dev_info for a character device.  It also removes the need for
the mtd_inodefs filesystem.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 32 insertions, 32 deletions

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 4c58333b4257..9a6b63783a94 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -287,13 +287,24 @@ static unsigned long get_unmapped_area_mem(struct file *file,
         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
-#define get_unmapped_area_mem   NULL
 
 static inline int private_mapping_ok(struct vm_area_struct *vma)
 {
@@ -721,7 +732,10 @@ static const struct file_operations mem_fops = {
         .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
 };
 
 #ifdef CONFIG_DEVKMEM
@@ -731,7 +745,10 @@ static const struct file_operations kmem_fops = {
         .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
 };
 #endif
 
@@ -760,16 +777,9 @@ static const struct file_operations zero_fops = {
         .read_iter      = read_iter_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,
+#ifndef CONFIG_MMU
+        .mmap_capabilities = zero_mmap_capabilities,
+#endif
 };
 
 static const struct file_operations full_fops = {
@@ -783,22 +793,22 @@ static const struct memdev {
         const char *name;
         umode_t mode;
         const struct file_operations *fops;
-        struct backing_dev_info *dev_info;
+        fmode_t fmode;
 } devlist[] = {
-         [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },
+         [1] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
 #ifdef CONFIG_DEVKMEM
-         [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
+         [2] = { "kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET },
 #endif
-         [3] = { "null", 0666, &null_fops, NULL },
+         [3] = { "null", 0666, &null_fops, 0 },
 #ifdef CONFIG_DEVPORT
-         [4] = { "port", 0, &port_fops, NULL },
+         [4] = { "port", 0, &port_fops, 0 },
 #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 },
+         [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, NULL },
+        [11] = { "kmsg", 0644, &kmsg_fops, 0 },
 #endif
 };
 
@@ -816,12 +826,7 @@ static int memory_open(struct inode *inode, struct file *filp)
                 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;
+        filp->f_mode |= dev->fmode;
 
         if (dev->fops->open)
                 return dev->fops->open(inode, filp);
@@ -846,11 +851,6 @@ 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);