shm: fix the filename of hugetlb sysv shared memory

Some user space tools need to identify SYSV shared memory when examining
/proc/<pid>/maps.  To do so they look for a block device with major zero, a
dentry named SYSV<sysv key>, and having the minor of the internal sysv
shared memory kernel mount.

To help these tools and to make it easier for people just browsing
/proc/<pid>/maps this patch modifies hugetlb sysv shared memory to use the
SYSV<key> dentry naming convention.

User space tools will still have to be aware that hugetlb sysv shared
memory lives on a different internal kernel mount and so has a different
block device minor number from the rest of sysv shared memory.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Albert Cahalan <acahalan@gmail.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/hugetlbfs/inode.c

@@ -736,15 +736,13 @@ static int can_do_hugetlb_shm(void)
 			can_do_mlock());
 }
 
-struct file *hugetlb_zero_setup(size_t size)
+struct file *hugetlb_file_setup(const char *name, size_t size)
 {
 	int error = -ENOMEM;
 	struct file *file;
 	struct inode *inode;
 	struct dentry *dentry, *root;
 	struct qstr quick_string;
-	char buf[16];
-	static atomic_t counter;
 
 	if (!hugetlbfs_vfsmount)
 		return ERR_PTR(-ENOENT);
@@ -756,8 +754,7 @@ struct file *hugetlb_zero_setup(size_t size)
 		return ERR_PTR(-ENOMEM);
 
 	root = hugetlbfs_vfsmount->mnt_root;
-	snprintf(buf, 16, "%u", atomic_inc_return(&counter));
-	quick_string.name = buf;
+	quick_string.name = name;
 	quick_string.len = strlen(quick_string.name);
 	quick_string.hash = 0;
 	dentry = d_alloc(root, &quick_string);

include/linux/hugetlb.h

@@ -163,7 +163,7 @@ static inline struct hugetlbfs_sb_info *HUGETLBFS_SB(struct super_block *sb)
 
 extern const struct file_operations hugetlbfs_file_operations;
 extern struct vm_operations_struct hugetlb_vm_ops;
-struct file *hugetlb_zero_setup(size_t);
+struct file *hugetlb_file_setup(const char *name, size_t);
 int hugetlb_get_quota(struct address_space *mapping);
 void hugetlb_put_quota(struct address_space *mapping);
 
@@ -185,7 +185,7 @@ static inline void set_file_hugepages(struct file *file)
 
 #define is_file_hugepages(file)		0
 #define set_file_hugepages(file)	BUG()
-#define hugetlb_zero_setup(size)	ERR_PTR(-ENOSYS)
+#define hugetlb_file_setup(name,size)	ERR_PTR(-ENOSYS)
 
 #endif /* !CONFIG_HUGETLBFS */
 

ipc/shm.c

@@ -366,9 +366,10 @@ static int newseg (struct ipc_namespace *ns, key_t key, int shmflg, size_t size)
 		return error;
 	}
 
+	sprintf (name, "SYSV%08x", key);
 	if (shmflg & SHM_HUGETLB) {
-		/* hugetlb_zero_setup takes care of mlock user accounting */
-		file = hugetlb_zero_setup(size);
+		/* hugetlb_file_setup takes care of mlock user accounting */
+		file = hugetlb_file_setup(name, size);
 		shp->mlock_user = current->user;
 	} else {
 		int acctflag = VM_ACCOUNT;
@@ -379,7 +380,6 @@ static int newseg (struct ipc_namespace *ns, key_t key, int shmflg, size_t size)
 		if  ((shmflg & SHM_NORESERVE) &&
 				sysctl_overcommit_memory != OVERCOMMIT_NEVER)
 			acctflag = 0;
-		sprintf (name, "SYSV%08x", key);
 		file = shmem_file_setup(name, size, acctflag);
 	}
 	error = PTR_ERR(file);