f2fs: give random value to i_generation

This follows to give random number to i_generation along with commit
23253068 ("ext4: improve smp scalability for inode generation")

This can be used for DUN for UFS HW encryption.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1242,8 +1242,6 @@ struct f2fs_sb_info {
 
 	unsigned int nquota_files;		/* # of quota sysfile */
 
-	u32 s_next_generation;			/* for NFS support */
-
 	/* # of pages, see count_type */
 	atomic_t nr_pages[NR_COUNT_TYPE];
 	/* # of allocated blocks */

fs/f2fs/namei.c

@@ -10,6 +10,7 @@
 #include <linux/pagemap.h>
 #include <linux/sched.h>
 #include <linux/ctype.h>
+#include <linux/random.h>
 #include <linux/dcache.h>
 #include <linux/namei.h>
 #include <linux/quotaops.h>
@@ -50,7 +51,7 @@ static struct inode *f2fs_new_inode(struct inode *dir, umode_t mode)
 	inode->i_blocks = 0;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 	F2FS_I(inode)->i_crtime = inode->i_mtime;
-	inode->i_generation = sbi->s_next_generation++;
+	inode->i_generation = prandom_u32();
 
 	if (S_ISDIR(inode->i_mode))
 		F2FS_I(inode)->i_current_depth = 1;

fs/f2fs/super.c

@@ -3129,7 +3129,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_maxbytes = sbi->max_file_blocks <<
 				le32_to_cpu(raw_super->log_blocksize);
 	sb->s_max_links = F2FS_LINK_MAX;
-	get_random_bytes(&sbi->s_next_generation, sizeof(u32));
 
 #ifdef CONFIG_QUOTA
 	sb->dq_op = &f2fs_quota_operations;