[PATCH 3/5] hugetlbfs: use call_once()

[PATCH 3/5] hugetlbfs: use call_once()

[Akinobu Mita]

This patch defers mounting hugetlbfs till hugetlb_file_setup() is
called first time by using call_once().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: William Irwin <wli@holomorphy.com>
---
 fs/hugetlbfs/inode.c |   30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

Index: 2.6-rc/fs/hugetlbfs/inode.c
===================================================================
--- 2.6-rc.orig/fs/hugetlbfs/inode.c
+++ 2.6-rc/fs/hugetlbfs/inode.c
@@ -31,6 +31,7 @@
 #include <linux/dnotify.h>
 #include <linux/statfs.h>
 #include <linux/security.h>
+#include <linux/once.h>
 
 #include <asm/uaccess.h>
 
@@ -903,6 +904,13 @@ static struct file_system_type hugetlbfs
 
 static struct vfsmount *hugetlbfs_vfsmount;
 
+static int init_hugetlbfs_vfsmount(void)
+{
+	hugetlbfs_vfsmount = kern_mount(&hugetlbfs_fs_type);
+
+	return IS_ERR(hugetlbfs_vfsmount) ? PTR_ERR(hugetlbfs_vfsmount) : 0;
+}
+
 static int can_do_hugetlb_shm(void)
 {
 	return likely(capable(CAP_IPC_LOCK) ||
@@ -912,14 +920,16 @@ static int can_do_hugetlb_shm(void)
 
 struct file *hugetlb_file_setup(const char *name, size_t size)
 {
-	int error = -ENOMEM;
+	int error;
 	struct file *file;
 	struct inode *inode;
 	struct dentry *dentry, *root;
 	struct qstr quick_string;
+	static DEFINE_ONCE(once);
 
-	if (!hugetlbfs_vfsmount)
-		return ERR_PTR(-ENOENT);
+	error = call_once(&once, init_hugetlbfs_vfsmount);
+	if (error)
+		return ERR_PTR(error);
 
 	if (!can_do_hugetlb_shm())
 		return ERR_PTR(-EPERM);
@@ -970,7 +980,6 @@ out_shm_unlock:
 static int __init init_hugetlbfs_fs(void)
 {
 	int error;
-	struct vfsmount *vfsmount;
 
 	error = bdi_init(&hugetlbfs_backing_dev_info);
 	if (error)
@@ -986,18 +995,9 @@ static int __init init_hugetlbfs_fs(void
 	if (error)
 		goto out;
 
-	vfsmount = kern_mount(&hugetlbfs_fs_type);
-
-	if (!IS_ERR(vfsmount)) {
-		hugetlbfs_vfsmount = vfsmount;
-		return 0;
-	}
-
-	error = PTR_ERR(vfsmount);
-
+	return 0;
  out:
-	if (error)
-		kmem_cache_destroy(hugetlbfs_inode_cachep);
+	kmem_cache_destroy(hugetlbfs_inode_cachep);
  out2:
 	bdi_destroy(&hugetlbfs_backing_dev_info);
 	return error;

[PATCH 4/5] shmem: use call_once()

[Akinobu Mita]

This patch defers mounting tmpfs till shmem_file_setup() is
called first time by using call_once().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 mm/shmem.c |   32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

Index: 2.6-rc/mm/shmem.c
===================================================================
--- 2.6-rc.orig/mm/shmem.c
+++ 2.6-rc/mm/shmem.c
@@ -50,6 +50,7 @@
 #include <linux/migrate.h>
 #include <linux/highmem.h>
 #include <linux/seq_file.h>
+#include <linux/once.h>
 
 #include <asm/uaccess.h>
 #include <asm/div64.h>
@@ -2520,7 +2521,6 @@ static struct file_system_type tmpfs_fs_
 	.get_sb		= shmem_get_sb,
 	.kill_sb	= kill_litter_super,
 };
-static struct vfsmount *shm_mnt;
 
 static int __init init_tmpfs(void)
 {
@@ -2540,27 +2540,29 @@ static int __init init_tmpfs(void)
 		goto out2;
 	}
 
-	shm_mnt = vfs_kern_mount(&tmpfs_fs_type, MS_NOUSER,
-				tmpfs_fs_type.name, NULL);
-	if (IS_ERR(shm_mnt)) {
-		error = PTR_ERR(shm_mnt);
-		printk(KERN_ERR "Could not kern_mount tmpfs\n");
-		goto out1;
-	}
 	return 0;
-
-out1:
-	unregister_filesystem(&tmpfs_fs_type);
 out2:
 	destroy_inodecache();
 out3:
 	bdi_destroy(&shmem_backing_dev_info);
 out4:
-	shm_mnt = ERR_PTR(error);
 	return error;
 }
 module_init(init_tmpfs)
 
+static struct vfsmount *shm_mnt;
+
+static int init_shm_mnt(void)
+{
+	shm_mnt = vfs_kern_mount(&tmpfs_fs_type, MS_NOUSER,
+				tmpfs_fs_type.name, NULL);
+	if (IS_ERR(shm_mnt)) {
+		printk(KERN_ERR "Could not kern_mount tmpfs\n");
+		return PTR_ERR(shm_mnt);
+	}
+	return 0;
+}
+
 /*
  * shmem_file_setup - get an unlinked file living in tmpfs
  *
@@ -2575,9 +2577,11 @@ struct file *shmem_file_setup(char *name
 	struct inode *inode;
 	struct dentry *dentry, *root;
 	struct qstr this;
+	static DEFINE_ONCE(once);
 
-	if (IS_ERR(shm_mnt))
-		return (void *)shm_mnt;
+	error = call_once(&once, init_shm_mnt);
+	if (error)
+		return ERR_PTR(error);
 
 	if (size < 0 || size > SHMEM_MAX_BYTES)
 		return ERR_PTR(-EINVAL);

[PATCH 5/5] tiny-shmem: use call_once()

[Akinobu Mita]

This patch defers mounting tmpfs till shmem_file_setup() is
called first time by using call_once().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 mm/tiny-shmem.c |   21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

Index: 2.6-rc/mm/tiny-shmem.c
===================================================================
--- 2.6-rc.orig/mm/tiny-shmem.c
+++ 2.6-rc/mm/tiny-shmem.c
@@ -19,6 +19,7 @@
 #include <linux/module.h>
 #include <linux/swap.h>
 #include <linux/ramfs.h>
+#include <linux/once.h>
 
 static struct file_system_type tmpfs_fs_type = {
 	.name		= "tmpfs",
@@ -26,19 +27,23 @@ static struct file_system_type tmpfs_fs_
 	.kill_sb	= kill_litter_super,
 };
 
-static struct vfsmount *shm_mnt;
-
 static int __init init_tmpfs(void)
 {
 	BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);
 
-	shm_mnt = kern_mount(&tmpfs_fs_type);
-	BUG_ON(IS_ERR(shm_mnt));
-
 	return 0;
 }
 module_init(init_tmpfs)
 
+static struct vfsmount *shm_mnt;
+
+static int init_shm_mnt(void)
+{
+	shm_mnt = kern_mount(&tmpfs_fs_type);
+
+	return IS_ERR(shm_mnt) ? PTR_ERR(shm_mnt) : 0;
+}
+
 /*
  * shmem_file_setup - get an unlinked file living in tmpfs
  *
@@ -53,9 +58,11 @@ struct file *shmem_file_setup(char *name
 	struct inode *inode;
 	struct dentry *dentry, *root;
 	struct qstr this;
+	static DEFINE_ONCE(once);
 
-	if (IS_ERR(shm_mnt))
-		return (void *)shm_mnt;
+	error = call_once(&once, init_shm_mnt);
+	if (error)
+		return ERR_PTR(error);
 
 	error = -ENOMEM;
 	this.name = name;

Re: [PATCH 4/5] shmem: use call_once()

[Hugh Dickins]

On Tue, 11 Mar 2008, Akinobu Mita wrote:
> This patch defers mounting tmpfs till shmem_file_setup() is
> called first time by using call_once().

Please explain why we might need this patch: is something changing
elsewhere?  Or are you misled by that "module_init(init_tmpfs)"
into thinking that mm/shmem.c is sometimes built modular?

Hugh

Re: [PATCH 4/5] shmem: use call_once()

[Akinobu Mita]

2008/3/11, Hugh Dickins <hugh@veritas.com>:
> On Tue, 11 Mar 2008, Akinobu Mita wrote:
>  > This patch defers mounting tmpfs till shmem_file_setup() is
>  > called first time by using call_once().
>
>
> Please explain why we might need this patch: is something changing
>  elsewhere?  Or are you misled by that "module_init(init_tmpfs)"
>  into thinking that mm/shmem.c is sometimes built modular?
>

If no processes call shmem_file_setup() (via shm_get(2)), it is unnecessary
to do vfs_kern_mount(&tmpfs_fs_type, ...) unconditionary in boot-time.
So I thought it is suitable example to demonstrate how to use "call_once()"
in this patch set.

Re: [PATCH 4/5] shmem: use call_once()

[Hugh Dickins]

On Tue, 11 Mar 2008, Akinobu Mita wrote:
> 2008/3/11, Hugh Dickins <hugh@veritas.com>:
> > On Tue, 11 Mar 2008, Akinobu Mita wrote:
> >  > This patch defers mounting tmpfs till shmem_file_setup() is
> >  > called first time by using call_once().
> >
> > Please explain why we might need this patch: is something changing
> >  elsewhere?  Or are you misled by that "module_init(init_tmpfs)"
> >  into thinking that mm/shmem.c is sometimes built modular?
> 
> If no processes call shmem_file_setup() (via shm_get(2)), it is unnecessary
                                       or shmem_zero_setup, not very common
> to do vfs_kern_mount(&tmpfs_fs_type, ...) unconditionary in boot-time.
> So I thought it is suitable example to demonstrate how to use "call_once()"
> in this patch set.

Oh, I see, thanks.  Well, I don't feel all that strongly about it; but
on the whole I'd prefer we leave it as part of the __init, than change
it around to provide this example (and risk introducing some weird issue
e.g. related to its "dev"?).  I guess the same should go for the huge
and the tiny, whereas you have better justification in the idr case.
Call me over-cautious.

Hugh