Patchwork [v3] mtd: Do not corrupt backing device of device node inode

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Submitter Kirill A. Shutemov
Date May 5, 2010, 8:21 a.m.
Message ID <1273047688-20947-1-git-send-email-kirill@shutemov.name>
Download mbox | patch
Permalink /patch/51672/
State New
Headers show

Comments

Kirill A. Shutemov - May 5, 2010, 8:21 a.m.
We cannot modify file->f_mapping->backing_dev_info, because it will corrupt
backing device of device node inode, since file->f_mapping is equal to
inode->i_mapping (see __dentry_open() in fs/open.c).

Let's introduce separate inode for MTD device with appropriate backing
device.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: Jan Kara <jack@suse.cz>

---
Changelog
 v2 -> v3:
  - Rebase to mtd.git.
 v1 -> v2:
  - Fix error handling based on comments by Jan Kara.

---
 drivers/mtd/mtdchar.c   |   77 ++++++++++++++++++++++++++++++++++++++++++-----
 drivers/mtd/mtdcore.c   |    3 ++
 include/linux/mtd/mtd.h |    3 ++
 3 files changed, 75 insertions(+), 8 deletions(-)
Artem Bityutskiy - May 5, 2010, 2:17 p.m.
On Wed, 2010-05-05 at 11:21 +0300, Kirill A. Shutemov wrote:
> We cannot modify file->f_mapping->backing_dev_info, because it will corrupt
> backing device of device node inode, since file->f_mapping is equal to
> inode->i_mapping (see __dentry_open() in fs/open.c).
> 
> Let's introduce separate inode for MTD device with appropriate backing
> device.
> 
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> Acked-by: Jan Kara <jack@suse.cz>

I get the following build error:

[dedekind@eru l2-mtd-2.6]$ make -j8
O=/home/dedekind/tmp/l2-mtd-2.6-x86_64/
  GEN     /home/dedekind/tmp/l2-mtd-2.6-x86_64/Makefile
  CHK     include/linux/version.h
  CHK     include/generated/utsrelease.h
  Using /home/dedekind/git/l2-mtd-2.6 as source for kernel
  CALL    /home/dedekind/git/l2-mtd-2.6/scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CHK     include/linux/version.h
make[3]: `scripts/unifdef' is up to date.
  Building modules, stage 2.
Kernel: arch/x86/boot/bzImage is ready  (#2)
  MODPOST 146 modules
ERROR: "__iget" [drivers/mtd/mtdchar.ko] undefined!
ERROR: "inode_lock" [drivers/mtd/mtdchar.ko] undefined!
make[2]: *** [__modpost] Error 1
make[1]: *** [modules] Error 2
make: *** [sub-make] Error 2

__iget and inode_lock are not exported...
Jan Kara - May 5, 2010, 2:27 p.m.
On Wed 05-05-10 17:17:19, Artem Bityutskiy wrote:
> On Wed, 2010-05-05 at 11:21 +0300, Kirill A. Shutemov wrote:
> > We cannot modify file->f_mapping->backing_dev_info, because it will corrupt
> > backing device of device node inode, since file->f_mapping is equal to
> > inode->i_mapping (see __dentry_open() in fs/open.c).
> > 
> > Let's introduce separate inode for MTD device with appropriate backing
> > device.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> > Acked-by: Jan Kara <jack@suse.cz>
> 
> I get the following build error:
> 
> [dedekind@eru l2-mtd-2.6]$ make -j8
> O=/home/dedekind/tmp/l2-mtd-2.6-x86_64/
>   GEN     /home/dedekind/tmp/l2-mtd-2.6-x86_64/Makefile
>   CHK     include/linux/version.h
>   CHK     include/generated/utsrelease.h
>   Using /home/dedekind/git/l2-mtd-2.6 as source for kernel
>   CALL    /home/dedekind/git/l2-mtd-2.6/scripts/checksyscalls.sh
>   CHK     include/generated/compile.h
>   CHK     include/linux/version.h
> make[3]: `scripts/unifdef' is up to date.
>   Building modules, stage 2.
> Kernel: arch/x86/boot/bzImage is ready  (#2)
>   MODPOST 146 modules
> ERROR: "__iget" [drivers/mtd/mtdchar.ko] undefined!
> ERROR: "inode_lock" [drivers/mtd/mtdchar.ko] undefined!
> make[2]: *** [__modpost] Error 1
> make[1]: *** [modules] Error 2
> make: *** [sub-make] Error 2
> 
> __iget and inode_lock are not exported...
  Ah, right. igrab() should be used instead of __iget inside the
inode_lock.

								Honza

Patch

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index c355491..a2bb3ce 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -15,12 +15,15 @@ 
 #include <linux/smp_lock.h>
 #include <linux/backing-dev.h>
 #include <linux/compat.h>
+#include <linux/mount.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/compatmac.h>
 
 #include <asm/uaccess.h>
 
+#define MTD_INODE_FS_MAGIC 0x11307854
+static struct vfsmount *mtd_inode_mnt __read_mostly;
 
 /*
  * Data structure to hold the pointer to the mtd device as well
@@ -85,11 +88,30 @@  static int mtd_open(struct inode *inode, struct file *file)
 		goto out;
 	}
 
-	if (mtd->backing_dev_info)
-		file->f_mapping->backing_dev_info = mtd->backing_dev_info;
+	if (!mtd->inode) {
+		mtd->inode = new_inode(mtd_inode_mnt->mnt_sb);
+		if (!mtd->inode) {
+			put_mtd_device(mtd);
+			ret = -ENOMEM;
+			goto out;
+		}
+		mtd->inode->i_mode = S_IFCHR;
+		mtd->inode->i_rdev = inode->i_rdev;
+		if (mtd->backing_dev_info) {
+			mtd->inode->i_data.backing_dev_info =
+				mtd->backing_dev_info;
+		}
+	}
+
+	spin_lock(&inode_lock);
+	__iget(mtd->inode);
+	spin_unlock(&inode_lock);
+
+	file->f_mapping = mtd->inode->i_mapping;
 
 	/* You can't open it RW if it's not a writeable device */
 	if ((file->f_mode & FMODE_WRITE) && !(mtd->flags & MTD_WRITEABLE)) {
+		iput(mtd->inode);
 		put_mtd_device(mtd);
 		ret = -EACCES;
 		goto out;
@@ -97,6 +119,7 @@  static int mtd_open(struct inode *inode, struct file *file)
 
 	mfi = kzalloc(sizeof(*mfi), GFP_KERNEL);
 	if (!mfi) {
+		iput(mtd->inode);
 		put_mtd_device(mtd);
 		ret = -ENOMEM;
 		goto out;
@@ -122,6 +145,8 @@  static int mtd_close(struct inode *inode, struct file *file)
 	if ((file->f_mode & FMODE_WRITE) && mtd->sync)
 		mtd->sync(mtd);
 
+	iput(mtd->inode);
+
 	put_mtd_device(mtd);
 	file->private_data = NULL;
 	kfree(mfi);
@@ -951,22 +976,58 @@  static const struct file_operations mtd_fops = {
 #endif
 };
 
+static int mtd_inodefs_get_sb(struct file_system_type *fs_type, int flags,
+                               const char *dev_name, void *data,
+                               struct vfsmount *mnt)
+{
+        return get_sb_pseudo(fs_type, "mtd_inode:", NULL, MTD_INODE_FS_MAGIC,
+                             mnt);
+}
+
+static struct file_system_type mtd_inodefs_type = {
+       .name = "mtd_inodefs",
+       .get_sb = mtd_inodefs_get_sb,
+       .kill_sb = kill_anon_super,
+};
+
 static int __init init_mtdchar(void)
 {
-	int status;
+	int ret;
 
-	status = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,
+	ret = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,
 				   "mtd", &mtd_fops);
-	if (status < 0) {
-		printk(KERN_NOTICE "Can't allocate major number %d for Memory Technology Devices.\n",
-		       MTD_CHAR_MAJOR);
+	if (ret < 0) {
+		pr_notice("Can't allocate major number %d for "
+				"Memory Technology Devices.\n", MTD_CHAR_MAJOR);
+		return ret;
+	}
+
+	ret = register_filesystem(&mtd_inodefs_type);
+	if (ret) {
+		pr_notice("Can't register mtd_inodefs filesystem: %d\n", ret);
+		goto err_unregister_chdev;
 	}
 
-	return status;
+	mtd_inode_mnt = kern_mount(&mtd_inodefs_type);
+	if (IS_ERR(mtd_inode_mnt)) {
+		ret = PTR_ERR(mtd_inode_mnt);
+		pr_notice("Error mounting mtd_inodefs filesystem: %d\n", ret);
+		goto err_unregister_filesystem;
+	}
+
+	return ret;
+
+err_unregister_filesystem:
+	unregister_filesystem(&mtd_inodefs_type);
+err_unregister_chdev:
+	unregister_chrdev(MTD_CHAR_MAJOR, "mtd");
+	return ret;
 }
 
 static void __exit cleanup_mtdchar(void)
 {
+	mntput(mtd_inode_mnt);
+	unregister_filesystem(&mtd_inodefs_type);
 	__unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
 }
 
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 70a7858..fa424ad 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -369,6 +369,9 @@  int del_mtd_device (struct mtd_info *mtd)
 		       mtd->index, mtd->name, mtd->usecount);
 		ret = -EBUSY;
 	} else {
+		if (mtd->inode)
+			iput(mtd->inode);
+
 		device_unregister(&mtd->dev);
 
 		idr_remove(&mtd_idr, mtd->index);
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 5326435..d66409a 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -12,6 +12,7 @@ 
 #include <linux/uio.h>
 #include <linux/notifier.h>
 #include <linux/device.h>
+#include <linux/fs.h>
 
 #include <linux/mtd/compatmac.h>
 #include <mtd/mtd-abi.h>
@@ -174,6 +175,8 @@  struct mtd_info {
 	 */
 	struct backing_dev_info *backing_dev_info;
 
+	/* inode for mtd device */
+	struct inode *inode;
 
 	int (*read) (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf);
 	int (*write) (struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf);