diff mbox series

[v3,2/5] ovl: allocate a container struct ovl_file for ovl private context

Message ID 20241007141925.327055-3-amir73il@gmail.com (mailing list archive)
State New
Headers show
Series Store overlay real upper file in ovl_file | expand

Commit Message

Amir Goldstein Oct. 7, 2024, 2:19 p.m. UTC 
Instead of using ->private_data to point at realfile directly, so
that we can add more context per ovl open file.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/file.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

Comments

Al Viro Oct. 7, 2024, 2:43 p.m. UTC | #1 
On Mon, Oct 07, 2024 at 04:19:22PM +0200, Amir Goldstein wrote:
> Instead of using ->private_data to point at realfile directly, so
> that we can add more context per ovl open file.

Hmm...  That'll cost you an extra deref to get to underlying file.
Cache footprint might get unpleasant...
Miklos Szeredi Oct. 7, 2024, 2:55 p.m. UTC | #2 
On Mon, 7 Oct 2024 at 16:43, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Mon, Oct 07, 2024 at 04:19:22PM +0200, Amir Goldstein wrote:
> > Instead of using ->private_data to point at realfile directly, so
> > that we can add more context per ovl open file.
>
> Hmm...  That'll cost you an extra deref to get to underlying file.
> Cache footprint might get unpleasant...

Yes, that's an extra deref.  But stacking is bound to greatly increase
the cache footprint anyway, so this doesn't look a serious worry to
me.  I don't think overlayfs is at the point where we are ready to
optimize at the cache access level.

Thanks,
Miklos
diff mbox series

Patch

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index f5d0498355d0..03bf6037b129 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -89,10 +89,15 @@  static int ovl_change_flags(struct file *file, unsigned int flags)
 	return 0;
 }
 
+struct ovl_file {
+	struct file *realfile;
+};
+
 static int ovl_real_fdget_path(const struct file *file, struct fd *real,
 			       struct path *realpath)
 {
-	struct file *realfile = file->private_data;
+	struct ovl_file *of = file->private_data;
+	struct file *realfile = of->realfile;
 
 	real->word = (unsigned long)realfile;
 
@@ -163,6 +168,7 @@  static int ovl_open(struct inode *inode, struct file *file)
 	struct dentry *dentry = file_dentry(file);
 	struct file *realfile;
 	struct path realpath;
+	struct ovl_file *of;
 	int err;
 
 	/* lazy lookup and verify lowerdata */
@@ -181,18 +187,28 @@  static int ovl_open(struct inode *inode, struct file *file)
 	if (!realpath.dentry)
 		return -EIO;
 
+	of = kzalloc(sizeof(struct ovl_file), GFP_KERNEL);
+	if (!of)
+		return -ENOMEM;
+
 	realfile = ovl_open_realfile(file, &realpath);
-	if (IS_ERR(realfile))
+	if (IS_ERR(realfile)) {
+		kfree(of);
 		return PTR_ERR(realfile);
+	}
 
-	file->private_data = realfile;
+	of->realfile = realfile;
+	file->private_data = of;
 
 	return 0;
 }
 
 static int ovl_release(struct inode *inode, struct file *file)
 {
-	fput(file->private_data);
+	struct ovl_file *of = file->private_data;
+
+	fput(of->realfile);
+	kfree(of);
 
 	return 0;
 }
@@ -427,14 +443,14 @@  static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	struct file *realfile = file->private_data;
+	struct ovl_file *of = file->private_data;
 	struct backing_file_ctx ctx = {
 		.cred = ovl_creds(file_inode(file)->i_sb),
 		.user_file = file,
 		.accessed = ovl_file_accessed,
 	};
 
-	return backing_file_mmap(realfile, vma, &ctx);
+	return backing_file_mmap(of->realfile, vma, &ctx);
 }
 
 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)