[PATCH] NOMMU: Make SYSV IPC SHM use ramfs facilities on NOMMU

The attached patch makes the SYSV IPC shared memory facilities use the new
ramfs facilities on a no-MMU kernel.

The following changes are made:

 (1) There are now shmem_mmap() and shmem_get_unmapped_area() functions to
     allow the IPC SHM facilities to commune with the tiny-shmem and shmem
     code.

 (2) ramfs files now need resizing using do_truncate() rather than by modifying
     the inode size directly (see shmem_file_setup()). This causes ramfs to
     attempt to bind a block of pages of sufficient size to the inode.

 (3) CONFIG_SYSVIPC is no longer contingent on CONFIG_MMU.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/mm.h

@@ -654,9 +654,18 @@ static inline struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
 }
 #endif
 struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags);
+extern int shmem_mmap(struct file *file, struct vm_area_struct *vma);
 
 int shmem_zero_setup(struct vm_area_struct *);
 
+#ifndef CONFIG_MMU
+extern unsigned long shmem_get_unmapped_area(struct file *file,
+					     unsigned long addr,
+					     unsigned long len,
+					     unsigned long pgoff,
+					     unsigned long flags);
+#endif
+
 static inline int can_do_mlock(void)
 {
 	if (capable(CAP_IPC_LOCK))

init/Kconfig

@@ -105,7 +105,6 @@ config SWAP
 
 config SYSVIPC
 	bool "System V IPC"
-	depends on MMU
 	---help---
 	  Inter Process Communication is a suite of library functions and
 	  system calls which let processes (running programs) synchronize and

ipc/shm.c

@@ -157,14 +157,22 @@ static void shm_close (struct vm_area_struct *shmd)
 
 static int shm_mmap(struct file * file, struct vm_area_struct * vma)
 {
-	file_accessed(file);
+	int ret;
+
+	ret = shmem_mmap(file, vma);
+	if (ret == 0) {
 		vma->vm_ops = &shm_vm_ops;
 		shm_inc(file->f_dentry->d_inode->i_ino);
-	return 0;
+	}
+
+	return ret;
 }
 
 static struct file_operations shm_file_operations = {
-	.mmap	= shm_mmap
+	.mmap	= shm_mmap,
+#ifndef CONFIG_MMU
+	.get_unmapped_area = shmem_get_unmapped_area,
+#endif
 };
 
 static struct vm_operations_struct shm_vm_ops = {

mm/nommu.c

@@ -1177,3 +1177,10 @@ int in_gate_area_no_task(unsigned long addr)
 {
 	return 0;
 }
+
+struct page *filemap_nopage(struct vm_area_struct *area,
+			unsigned long address, int *type)
+{
+	BUG();
+	return NULL;
+}

mm/shmem.c

@@ -1270,7 +1270,7 @@ out_nomem:
 	return retval;
 }
 
-static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
+int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	file_accessed(file);
 	vma->vm_ops = &shmem_vm_ops;

mm/tiny-shmem.c

@@ -81,13 +81,19 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
 		goto close_file;
 
 	d_instantiate(dentry, inode);
-	inode->i_size = size;
 	inode->i_nlink = 0;	/* It is unlinked */
+
 	file->f_vfsmnt = mntget(shm_mnt);
 	file->f_dentry = dentry;
 	file->f_mapping = inode->i_mapping;
 	file->f_op = &ramfs_file_operations;
 	file->f_mode = FMODE_WRITE | FMODE_READ;
+
+	/* notify everyone as to the change of file size */
+	error = do_truncate(dentry, size, file);
+	if (error < 0)
+		goto close_file;
+
 	return file;
 
 close_file:
@@ -123,3 +129,24 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
 {
 	return 0;
 }
+
+int shmem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	file_accessed(file);
+#ifndef CONFIG_MMU
+	return ramfs_nommu_mmap(file, vma);
+#else
+	return 0;
+#endif
+}
+
+#ifndef CONFIG_MMU
+unsigned long shmem_get_unmapped_area(struct file *file,
+				      unsigned long addr,
+				      unsigned long len,
+				      unsigned long pgoff,
+				      unsigned long flags)
+{
+	return ramfs_nommu_get_unmapped_area(file, addr, len, pgoff, flags);
+}
+#endif