[patch 2/2] hugetlb: add /dev/hugetlb char device

[patch 2/2] hugetlb: add /dev/hugetlb char device

[Ken Chen]

add a char device /dev/hugetlb that behaves similar to /dev/zero,
built on top of internal hugetlbfs mount.

Signed-off-by: Ken Chen <kenchen@google.com>


diff -u b/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
--- b/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -795,6 +795,23 @@
 	return ERR_PTR(error);
 }

+int hugetlb_zero_setup(struct file *file, struct vm_area_struct *vma)
+{
+	file = hugetlb_file_setup(vma->vm_end - vma->vm_start, 0);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	if (vma->vm_file)
+		fput(vma->vm_file);
+	vma->vm_file = file;
+	return hugetlbfs_file_mmap(file, vma);
+}
+
+const struct file_operations hugetlb_dev_fops = {
+	.mmap			= hugetlb_zero_setup,
+	.get_unmapped_area	= hugetlb_get_unmapped_area,
+};
+
 static int __init init_hugetlbfs_fs(void)
 {
 	int error;
diff -u b/include/linux/hugetlb.h b/include/linux/hugetlb.h
--- b/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -162,6 +162,7 @@
 }

 extern const struct file_operations hugetlbfs_file_operations;
+extern const struct file_operations hugetlb_dev_fops;
 extern struct vm_operations_struct hugetlb_vm_ops;
 struct file *hugetlb_file_setup(size_t, int);
 int hugetlb_get_quota(struct address_space *mapping);
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -27,6 +27,7 @@ #include <linux/backing-dev.h>
 #include <linux/bootmem.h>
 #include <linux/pipe_fs_i.h>
 #include <linux/pfn.h>
+#include <linux/hugetlb.h>

 #include <asm/uaccess.h>
 #include <asm/io.h>
@@ -939,6 +940,12 @@ #ifdef CONFIG_CRASH_DUMP
 			filp->f_op = &oldmem_fops;
 			break;
 #endif
+#ifdef CONFIG_HUGETLBFS
+		case 13:
+			printk("open hugetlb dev device\n");
+			filp->f_op = &hugetlb_dev_fops;
+			break;
+#endif
 		default:
 			return -ENXIO;
 	}
@@ -971,6 +978,9 @@ #endif
 #ifdef CONFIG_CRASH_DUMP
 	{12,"oldmem",    S_IRUSR | S_IWUSR | S_IRGRP, &oldmem_fops},
 #endif
+#ifdef CONFIG_HUGETLBFS
+	{13, "hugetlb",S_IRUGO | S_IWUGO,	    &hugetlb_dev_fops},
+#endif
 };

 static struct class *mem_class;

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Re: [patch 2/2] hugetlb: add /dev/hugetlb char device

[Christoph Hellwig]

> +int hugetlb_zero_setup(struct file *file, struct vm_area_struct *vma)
> +{
> +	file = hugetlb_file_setup(vma->vm_end - vma->vm_start, 0);
> +	if (IS_ERR(file))
> +		return PTR_ERR(file);
> +
> +	if (vma->vm_file)
> +		fput(vma->vm_file);
> +	vma->vm_file = file;
> +	return hugetlbfs_file_mmap(file, vma);
> +}

Setting vma->vm_file to something that is not the file we called mmap
on and even refers to a different inode seems rather dangerous.

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