From: David Howells <[email protected]>
Set the backing device info capabilities for /dev/mem and /dev/kmem to permit
direct sharing under no-MMU conditions and full mapping capabilities under MMU
conditions. Make the BDI used by these available to all directly mappable
character devices.
Also comment the capabilities for /dev/zero.
Signed-Off-By: David Howells <[email protected]>
---
drivers/char/mem.c | 33 +++++++++++++++++++++++++++++++++
fs/char_dev.c | 20 ++++++++++++++++++++
include/linux/cdev.h | 2 ++
3 files changed, 55 insertions(+), 0 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 917b204..48bdf6b 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -238,6 +238,19 @@ #endif
}
#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;
+}
+#endif
+
static int mmap_mem(struct file * file, struct vm_area_struct * vma)
{
size_t size = vma->vm_end - vma->vm_start;
@@ -245,6 +258,12 @@ static int mmap_mem(struct file * file,
if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
return -EINVAL;
+#ifndef CONFIG_MMU
+ /* can't do an in-place private mapping if there's no MMU */
+ if (!(vma->vm_flags & VM_MAYSHARE))
+ return -ENOSYS;
+#endif
+
vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
size,
vma->vm_page_prot);
@@ -782,6 +801,9 @@ static const struct file_operations mem_
.write = write_mem,
.mmap = mmap_mem,
.open = open_mem,
+#ifndef CONFIG_MMU
+ .get_unmapped_area = get_unmapped_area_mem,
+#endif
};
static const struct file_operations kmem_fops = {
@@ -790,6 +812,9 @@ static const struct file_operations kmem
.write = write_kmem,
.mmap = mmap_kmem,
.open = open_kmem,
+#ifndef CONFIG_MMU
+ .get_unmapped_area = get_unmapped_area_mem,
+#endif
};
static const struct file_operations null_fops = {
@@ -815,6 +840,10 @@ static const struct file_operations zero
.mmap = mmap_zero,
};
+/*
+ * capabilities for /dev/zero
+ * - permits private mappings, "copies" are taken of the source of zeros
+ */
static struct backing_dev_info zero_bdi = {
.capabilities = BDI_CAP_MAP_COPY,
};
@@ -862,9 +891,13 @@ static int memory_open(struct inode * in
switch (iminor(inode)) {
case 1:
filp->f_op = &mem_fops;
+ filp->f_mapping->backing_dev_info =
+ &directly_mappable_cdev_bdi;
break;
case 2:
filp->f_op = &kmem_fops;
+ filp->f_mapping->backing_dev_info =
+ &directly_mappable_cdev_bdi;
break;
case 3:
filp->f_op = &null_fops;
diff --git a/fs/char_dev.c b/fs/char_dev.c
index 3483d3c..0009346 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -19,11 +19,30 @@ #include <linux/kobject.h>
#include <linux/kobj_map.h>
#include <linux/cdev.h>
#include <linux/mutex.h>
+#include <linux/backing-dev.h>
#ifdef CONFIG_KMOD
#include <linux/kmod.h>
#endif
+/*
+ * capabilities for /dev/mem, /dev/kmem and similar directly mappable character
+ * devices
+ * - permits shared-mmap for read, write and/or exec
+ * - does not permit private mmap in NOMMU mode (can't do COW)
+ * - no readahead or I/O queue unplugging required
+ */
+struct backing_dev_info directly_mappable_cdev_bdi = {
+ .capabilities = (
+#ifdef CONFIG_MMU
+ /* permit private copies of the data to be taken */
+ BDI_CAP_MAP_COPY |
+#endif
+ /* permit direct mmap, for read, write or exec */
+ BDI_CAP_MAP_DIRECT |
+ BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
+};
+
static struct kobj_map *cdev_map;
static DEFINE_MUTEX(chrdevs_lock);
@@ -461,3 +480,4 @@ EXPORT_SYMBOL(cdev_del);
EXPORT_SYMBOL(cdev_add);
EXPORT_SYMBOL(register_chrdev);
EXPORT_SYMBOL(unregister_chrdev);
+EXPORT_SYMBOL(directly_mappable_cdev_bdi);
diff --git a/include/linux/cdev.h b/include/linux/cdev.h
index 2216638..ee5f53f 100644
--- a/include/linux/cdev.h
+++ b/include/linux/cdev.h
@@ -23,5 +23,7 @@ void cdev_del(struct cdev *);
void cd_forget(struct inode *);
+extern struct backing_dev_info directly_mappable_cdev_bdi;
+
#endif
#endif
-
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