[PATCH v2 3/5] shmem: Add a per-directory xarray

[Chuck Lever <cel@xxxxxxxxxx>]

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

Add the infrastructure for managing a per-directory
directory-offset-to-dentry map. For the moment it is unused.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 include/linux/shmem_fs.h |    2 ++
 mm/shmem.c               |   28 ++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 9029abd29b1c..c1a12eac778d 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -27,6 +27,8 @@ struct shmem_inode_info {
 	atomic_t		stop_eviction;	/* hold when working on inode */
 	struct timespec64	i_crtime;	/* file creation time */
 	unsigned int		fsflags;	/* flags for FS_IOC_[SG]ETFLAGS */
+	struct xarray		doff_map;	/* dir offset to entry mapping */
+	u32			next_doff;
 	struct inode		vfs_inode;
 };
 
diff --git a/mm/shmem.c b/mm/shmem.c
index e48a0947bcaf..b78253996108 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -40,6 +40,8 @@
 #include <linux/fs_parser.h>
 #include <linux/swapfile.h>
 #include <linux/iversion.h>
+#include <linux/xarray.h>
+
 #include "swap.h"
 
 static struct vfsmount *shm_mnt;
@@ -2412,6 +2414,8 @@ static struct inode *shmem_get_inode(struct mnt_idmap *idmap, struct super_block
 			inode->i_size = 2 * BOGO_DIRENT_SIZE;
 			inode->i_op = &shmem_dir_inode_operations;
 			inode->i_fop = &shmem_dir_operations;
+			xa_init_flags(&info->doff_map, XA_FLAGS_ALLOC1);
+			info->next_doff = 0;
 			break;
 		case S_IFLNK:
 			/*
@@ -2930,6 +2934,22 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
 	return 0;
 }
 
+static struct xarray *shmem_doff_map(struct inode *dir)
+{
+	return &SHMEM_I(dir)->doff_map;
+}
+
+/*
+ * During fs teardown (eg. umount), a directory's doff_map might still
+ * contain entries. xa_destroy() cleans out anything that remains.
+ */
+static void shmem_doff_map_destroy(struct inode *inode)
+{
+	struct xarray *xa = shmem_doff_map(inode);
+
+	xa_destroy(xa);
+}
+
 /*
  * File creation. Allocate an inode, and we're done..
  */
@@ -3905,6 +3925,12 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
 	return 0;
 }
 
+#else /* CONFIG_TMPFS */
+
+static inline void shmem_doff_map_destroy(struct inode *dir)
+{
+}
+
 #endif /* CONFIG_TMPFS */
 
 static void shmem_put_super(struct super_block *sb)
@@ -4052,6 +4078,8 @@ static void shmem_destroy_inode(struct inode *inode)
 {
 	if (S_ISREG(inode->i_mode))
 		mpol_free_shared_policy(&SHMEM_I(inode)->policy);
+	if (S_ISDIR(inode->i_mode))
+		shmem_doff_map_destroy(inode);
 }
 
 static void shmem_init_inode(void *foo)