[PATCH v4] tmpfs: support for file creation time

[Xavier Roche <xavier.roche@algolia.com>]

Various filesystems (including ext4) now support file creation time.
This patch adds such support for tmpfs-based filesystems.

Note that using shmem_getattr() on other file types than regular requires
that shmem_is_huge() check type, to stop incorrect HPAGE_PMD_SIZE blksize.

Signed-off-by: Xavier Roche <xavier.roche@algolia.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Jean Delvare <jdelvare@suse.de>
Tested-by: Xavier Roche <xavier.roche@algolia.com>
Tested-by: Sylvain Bellone <sylvain.bellone@algolia.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reported-by: Xavier Grand <xavier.grand@algolia.com>
Cc: Xavier Roche <xavier.roche@algolia.com>
Cc: Jean Delvare <jdelvare@suse.de>
Link: https://lore.kernel.org/lkml/b954973a-b8d1-cab8-63bd-6ea8063de3@google.com/
---
 include/linux/shmem_fs.h |  1 +
 mm/shmem.c               | 16 +++++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index e65b80ed09e7..ab51d3cd39bd 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -24,6 +24,7 @@ struct shmem_inode_info {
 	struct shared_policy	policy;		/* NUMA memory alloc policy */
 	struct simple_xattrs	xattrs;		/* list of xattrs */
 	atomic_t		stop_eviction;	/* hold when working on inode */
+	struct timespec64	i_crtime;	/* file creation time */
 	struct inode		vfs_inode;
 };
 
diff --git a/mm/shmem.c b/mm/shmem.c
index a09b29ec2b45..f8205b2b0322 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -476,6 +476,8 @@ bool shmem_is_huge(struct vm_area_struct *vma,
 {
 	loff_t i_size;
 
+	if (!S_ISREG(inode->i_mode))
+		return false;
 	if (shmem_huge == SHMEM_HUGE_DENY)
 		return false;
 	if (vma && ((vma->vm_flags & VM_NOHUGEPAGE) ||
@@ -1061,6 +1063,12 @@ static int shmem_getattr(struct user_namespace *mnt_userns,
 	if (shmem_is_huge(NULL, inode, 0))
 		stat->blksize = HPAGE_PMD_SIZE;
 
+	if (request_mask & STATX_BTIME) {
+		stat->result_mask |= STATX_BTIME;
+		stat->btime.tv_sec = info->i_crtime.tv_sec;
+		stat->btime.tv_nsec = info->i_crtime.tv_nsec;
+	}
+
 	return 0;
 }
 
@@ -1854,9 +1862,6 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 		return 0;
 	}
 
-	/* Never use a huge page for shmem_symlink() */
-	if (S_ISLNK(inode->i_mode))
-		goto alloc_nohuge;
 	if (!shmem_is_huge(vma, inode, index))
 		goto alloc_nohuge;
 
@@ -2265,6 +2270,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 		atomic_set(&info->stop_eviction, 0);
 		info->seals = F_SEAL_SEAL;
 		info->flags = flags & VM_NORESERVE;
+		info->i_crtime = inode->i_mtime;
 		INIT_LIST_HEAD(&info->shrinklist);
 		INIT_LIST_HEAD(&info->swaplist);
 		simple_xattrs_init(&info->xattrs);
@@ -3196,6 +3202,7 @@ static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
 #endif /* CONFIG_TMPFS_XATTR */
 
 static const struct inode_operations shmem_short_symlink_operations = {
+	.getattr	= shmem_getattr,
 	.get_link	= simple_get_link,
 #ifdef CONFIG_TMPFS_XATTR
 	.listxattr	= shmem_listxattr,
@@ -3203,6 +3210,7 @@ static const struct inode_operations shmem_short_symlink_operations = {
 };
 
 static const struct inode_operations shmem_symlink_inode_operations = {
+	.getattr	= shmem_getattr,
 	.get_link	= shmem_get_link,
 #ifdef CONFIG_TMPFS_XATTR
 	.listxattr	= shmem_listxattr,
@@ -3790,6 +3798,7 @@ static const struct inode_operations shmem_inode_operations = {
 
 static const struct inode_operations shmem_dir_inode_operations = {
 #ifdef CONFIG_TMPFS
+	.getattr	= shmem_getattr,
 	.create		= shmem_create,
 	.lookup		= simple_lookup,
 	.link		= shmem_link,
@@ -3811,6 +3820,7 @@ static const struct inode_operations shmem_dir_inode_operations = {
 };
 
 static const struct inode_operations shmem_special_inode_operations = {
+	.getattr	= shmem_getattr,
 #ifdef CONFIG_TMPFS_XATTR
 	.listxattr	= shmem_listxattr,
 #endif
-- 
2.25.1