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Subject[PATCH 1/2] NOMMU: Set BDI capabilities for /dev/mem and /dev/kmem
Date
From: David Howells <dhowells@redhat.com>

Set the backing device info capabilities for /dev/mem and /dev/kmem to permit
direct sharing under no-MMU conditions.

Also comment the capabilities for /dev/zero.

Signed-Off-By: David Howells <dhowells@redhat.com>
---
drivers/char/mem.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 files changed, 42 insertions(+), 0 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 917b204..4c29619 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 = {
@@ -815,10 +840,25 @@ 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,
};

+/*
+ * capabilities for /dev/mem and /dev/kmem
+ * - permits shared mmap for read, write and/or exec
+ * - does not permit private mmap (add BDI_CAP_MAP_COPY to permit this)
+ */
+static struct backing_dev_info mem_bdi = {
+ .capabilities = (BDI_CAP_MAP_DIRECT |
+ BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP |
+ BDI_CAP_EXEC_MAP),
+};
+
static const struct file_operations full_fops = {
.llseek = full_lseek,
.read = read_full,
@@ -861,9 +901,11 @@ static int memory_open(struct inode * in
{
switch (iminor(inode)) {
case 1:
+ filp->f_mapping->backing_dev_info = &mem_bdi;
filp->f_op = &mem_fops;
break;
case 2:
+ filp->f_mapping->backing_dev_info = &mem_bdi;
filp->f_op = &kmem_fops;
break;
case 3:
-
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