fuse: add cache_mask

If writeback_cache is enabled, then the size, mtime and ctime attributes of
regular files are always valid in the kernel's cache.  They are retrieved
from userspace only when the inode is freshly looked up.

Add a more generic "cache_mask", that indicates which attributes are
currently valid in cache.

This patch doesn't change behavior.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -1667,7 +1667,8 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
 	}
 
 	fuse_change_attributes_common(inode, &outarg.attr,
-				      attr_timeout(&outarg));
+				      attr_timeout(&outarg),
+				      fuse_get_cache_mask(inode));
 	oldsize = inode->i_size;
 	/* see the comment in fuse_change_attributes() */
 	if (!is_wb || is_truncate)

fs/fuse/fuse_i.h

@@ -1031,7 +1031,9 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 			    u64 attr_valid, u64 attr_version);
 
 void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
-				   u64 attr_valid);
+				   u64 attr_valid, u32 cache_mask);
+
+u32 fuse_get_cache_mask(struct inode *inode);
 
 /**
  * Initialize the client device

fs/fuse/inode.c

@@ -164,7 +164,7 @@ static ino_t fuse_squash_ino(u64 ino64)
 }
 
 void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
-				   u64 attr_valid)
+				   u64 attr_valid, u32 cache_mask)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_inode *fi = get_fuse_inode(inode);
@@ -184,9 +184,11 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 	inode->i_atime.tv_sec   = attr->atime;
 	inode->i_atime.tv_nsec  = attr->atimensec;
 	/* mtime from server may be stale due to local buffered write */
-	if (!fc->writeback_cache || !S_ISREG(inode->i_mode)) {
+	if (!(cache_mask & STATX_MTIME)) {
 		inode->i_mtime.tv_sec   = attr->mtime;
 		inode->i_mtime.tv_nsec  = attr->mtimensec;
+	}
+	if (!(cache_mask & STATX_CTIME)) {
 		inode->i_ctime.tv_sec   = attr->ctime;
 		inode->i_ctime.tv_nsec  = attr->ctimensec;
 	}
@@ -218,12 +220,22 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 	inode->i_flags &= ~S_NOSEC;
 }
 
+u32 fuse_get_cache_mask(struct inode *inode)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	if (!fc->writeback_cache || !S_ISREG(inode->i_mode))
+		return 0;
+
+	return STATX_MTIME | STATX_CTIME | STATX_SIZE;
+}
+
 void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 			    u64 attr_valid, u64 attr_version)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_inode *fi = get_fuse_inode(inode);
-	bool is_wb = fc->writeback_cache && S_ISREG(inode->i_mode);
+	u32 cache_mask;
 	loff_t oldsize;
 	struct timespec64 old_mtime;
 
@@ -233,10 +245,15 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 	 * may update i_size.  In these cases trust the cached value in the
 	 * inode.
 	 */
-	if (is_wb) {
+	cache_mask = fuse_get_cache_mask(inode);
+	if (cache_mask & STATX_SIZE)
 		attr->size = i_size_read(inode);
+
+	if (cache_mask & STATX_MTIME) {
 		attr->mtime = inode->i_mtime.tv_sec;
 		attr->mtimensec = inode->i_mtime.tv_nsec;
+	}
+	if (cache_mask & STATX_CTIME) {
 		attr->ctime = inode->i_ctime.tv_sec;
 		attr->ctimensec = inode->i_ctime.tv_nsec;
 	}
@@ -248,7 +265,7 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 	}
 
 	old_mtime = inode->i_mtime;
-	fuse_change_attributes_common(inode, attr, attr_valid);
+	fuse_change_attributes_common(inode, attr, attr_valid, cache_mask);
 
 	oldsize = inode->i_size;
 	/*
@@ -256,11 +273,11 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 	 * extend local i_size without keeping userspace server in sync. So,
 	 * attr->size coming from server can be stale. We cannot trust it.
 	 */
-	if (!is_wb)
+	if (!(cache_mask & STATX_SIZE))
 		i_size_write(inode, attr->size);
 	spin_unlock(&fi->lock);
 
-	if (!is_wb && S_ISREG(inode->i_mode)) {
+	if (!cache_mask && S_ISREG(inode->i_mode)) {
 		bool inval = false;
 
 		if (oldsize != attr->size) {