[PATCH 3/3] shmem: Add support for using full width of ino_t

[Chris Down]

The new inode64 option now uses get_next_ino_full, which always uses the
full width of ino_t (as opposed to get_next_ino, which always uses
unsigned int).

Using inode64 makes inode number wraparound significantly less likely,
at the cost of making some features that rely on the underlying
filesystem not setting any of the highest 32 bits (eg. overlayfs' xino)
not usable.

Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
Reported-by: Phyllipe Medeiros <phyllipe@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kernel-team@xxxxxx
---
 include/linux/shmem_fs.h |  1 +
 mm/shmem.c               | 41 ++++++++++++++++++++++++++++++++++++++--
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index de8e4b71e3ba..d7727d0d687f 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -35,6 +35,7 @@ struct shmem_sb_info {
 	unsigned char huge;	    /* Whether to try for hugepages */
 	kuid_t uid;		    /* Mount uid for root directory */
 	kgid_t gid;		    /* Mount gid for root directory */
+	bool small_inums;	    /* i_ino width unsigned int or ino_t */
 	struct mempolicy *mpol;     /* default memory policy for mappings */
 	spinlock_t shrinklist_lock;   /* Protects shrinklist */
 	struct list_head shrinklist;  /* List of shinkable inodes */
diff --git a/mm/shmem.c b/mm/shmem.c
index ff041cb15550..56cf581ec66d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -115,11 +115,13 @@ struct shmem_options {
 	kuid_t uid;
 	kgid_t gid;
 	umode_t mode;
+	bool small_inums;
 	int huge;
 	int seen;
 #define SHMEM_SEEN_BLOCKS 1
 #define SHMEM_SEEN_INODES 2
 #define SHMEM_SEEN_HUGE 4
+#define SHMEM_SEEN_INUMS 8
 };
 
 #ifdef CONFIG_TMPFS
@@ -2248,8 +2250,12 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 	inode = new_inode(sb);
 	if (inode) {
 		/* Recycle to avoid 32-bit wraparound where possible */
-		if (!inode->i_ino)
-			inode->i_ino = get_next_ino();
+		if (!inode->i_ino) {
+			if (sbinfo->small_inums)
+				inode->i_ino = get_next_ino();
+			else
+				inode->i_ino = get_next_ino_full();
+		}
 		inode_init_owner(inode, dir, mode);
 		inode->i_blocks = 0;
 		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
@@ -3380,6 +3386,8 @@ enum shmem_param {
 	Opt_nr_inodes,
 	Opt_size,
 	Opt_uid,
+	Opt_inode32,
+	Opt_inode64,
 };
 
 static const struct fs_parameter_spec shmem_param_specs[] = {
@@ -3391,6 +3399,8 @@ static const struct fs_parameter_spec shmem_param_specs[] = {
 	fsparam_string("nr_inodes",	Opt_nr_inodes),
 	fsparam_string("size",		Opt_size),
 	fsparam_u32   ("uid",		Opt_uid),
+	fsparam_flag  ("inode32",	Opt_inode32),
+	fsparam_flag  ("inode64",	Opt_inode64),
 	{}
 };
 
@@ -3415,6 +3425,7 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 	unsigned long long size;
 	char *rest;
 	int opt;
+	const char *err;
 
 	opt = fs_parse(fc, &shmem_fs_parameters, param, &result);
 	if (opt < 0)
@@ -3476,6 +3487,18 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 			break;
 		}
 		goto unsupported_parameter;
+	case Opt_inode32:
+		ctx->small_inums = true;
+		ctx->seen |= SHMEM_SEEN_INUMS;
+		break;
+	case Opt_inode64:
+		if (sizeof(ino_t) < 8) {
+			err = "Cannot use inode64 with <64bit inums in kernel";
+			goto err_msg;
+		}
+		ctx->small_inums = false;
+		ctx->seen |= SHMEM_SEEN_INUMS;
+		break;
 	}
 	return 0;
 
@@ -3483,6 +3506,8 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 	return invalf(fc, "tmpfs: Unsupported parameter '%s'", param->key);
 bad_value:
 	return invalf(fc, "tmpfs: Bad value for '%s'", param->key);
+err_msg:
+	return invalf(fc, "tmpfs: %s", err);
 }
 
 static int shmem_parse_options(struct fs_context *fc, void *data)
@@ -3567,6 +3592,15 @@ static int shmem_reconfigure(struct fs_context *fc)
 		}
 	}
 
+	/*
+	 * get_next_ino and get_next_ino_full have different static counters, so
+	 * it's not safe to change once we started or we could get duplicates
+	 */
+	if (ctx->seen & SHMEM_SEEN_INUMS) {
+		err = "Cannot retroactively change inode number size";
+		goto out;
+	}
+
 	if (ctx->seen & SHMEM_SEEN_HUGE)
 		sbinfo->huge = ctx->huge;
 	if (ctx->seen & SHMEM_SEEN_BLOCKS)
@@ -3608,6 +3642,7 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
 	if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
 		seq_printf(seq, ",gid=%u",
 				from_kgid_munged(&init_user_ns, sbinfo->gid));
+	seq_printf(seq, ",inode%d", (sbinfo->small_inums ? 32 : 64));
 #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
 	/* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
 	if (sbinfo->huge)
@@ -3667,6 +3702,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 	sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes;
 	sbinfo->uid = ctx->uid;
 	sbinfo->gid = ctx->gid;
+	sbinfo->small_inums = ctx->small_inums;
 	sbinfo->mode = ctx->mode;
 	sbinfo->huge = ctx->huge;
 	sbinfo->mpol = ctx->mpol;
@@ -3879,6 +3915,7 @@ int shmem_init_fs_context(struct fs_context *fc)
 	ctx->mode = 0777 | S_ISVTX;
 	ctx->uid = current_fsuid();
 	ctx->gid = current_fsgid();
+	ctx->small_inums = true;
 
 	fc->fs_private = ctx;
 	fc->ops = &shmem_fs_context_ops;
-- 
2.24.1