[RFC PATCH v3 1/5] KVM: guest_memfd: Refactor out kvm_gmem_alloc_file()

[Tao Gong]

From: Ackerley Tng <ackerleytng@xxxxxxxxxx>

The file represents a KVM instance's view into the underlying memory
that is managed by the guest_memfd inode. Refactoring out the file
creation enables this function to be reused when creating multiple views
into the same guest_memfd inode.

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Co-developed-by: Ryan Afranji <afranji@xxxxxxxxxx>
Signed-off-by: Ryan Afranji <afranji@xxxxxxxxxx>
Co-developed-by: Tao Gong <gongtao@xxxxxxxxxx>
Signed-off-by: Tao Gong <gongtao@xxxxxxxxxx>
---
 virt/kvm/guest_memfd.c | 67 +++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 27 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 93f3d29d5751a..3ca6f64d48040 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -937,10 +937,47 @@ static int kvm_gmem_init_inode(struct inode *inode, loff_t size, u64 flags)
 	return r;
 }
 
+/*
+ * Allocate a new guest_memfd file for @kvm that refers to @inode.  On success,
+ * the returned file takes over the caller's reference to @inode.
+ */
+static struct file *kvm_gmem_alloc_file(struct kvm *kvm, struct inode *inode,
+					const char *name)
+{
+	struct gmem_file *f;
+	struct file *file;
+
+	f = kzalloc_obj(*f);
+	if (!f)
+		return ERR_PTR(-ENOMEM);
+
+	/* __fput() will take care of fops_put(). */
+	if (!fops_get(&kvm_gmem_fops)) {
+		kfree(f);
+		return ERR_PTR(-ENOENT);
+	}
+
+	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops);
+	if (IS_ERR(file)) {
+		fops_put(&kvm_gmem_fops);
+		kfree(f);
+		return file;
+	}
+
+	file->f_flags |= O_LARGEFILE;
+	file->private_data = f;
+
+	kvm_get_kvm(kvm);
+	f->kvm = kvm;
+	xa_init(&f->bindings);
+	list_add(&f->entry, &GMEM_I(inode)->gmem_file_list);
+
+	return file;
+}
+
 static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 {
 	static const char *name = "[kvm-gmem]";
-	struct gmem_file *f;
 	struct inode *inode;
 	struct file *file;
 	int fd, err;
@@ -949,51 +986,27 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 	if (fd < 0)
 		return fd;
 
-	f = kzalloc_obj(*f);
-	if (!f) {
-		err = -ENOMEM;
-		goto err_fd;
-	}
-
-	/* __fput() will take care of fops_put(). */
-	if (!fops_get(&kvm_gmem_fops)) {
-		err = -ENOENT;
-		goto err_gmem;
-	}
-
 	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
 	if (IS_ERR(inode)) {
 		err = PTR_ERR(inode);
-		goto err_fops;
+		goto err_fd;
 	}
 
 	err = kvm_gmem_init_inode(inode, size, flags);
 	if (err)
 		goto err_inode;
 
-	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops);
+	file = kvm_gmem_alloc_file(kvm, inode, name);
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);
 		goto err_inode;
 	}
 
-	file->f_flags |= O_LARGEFILE;
-	file->private_data = f;
-
-	kvm_get_kvm(kvm);
-	f->kvm = kvm;
-	xa_init(&f->bindings);
-	list_add(&f->entry, &GMEM_I(inode)->gmem_file_list);
-
 	fd_install(fd, file);
 	return fd;
 
 err_inode:
 	iput(inode);
-err_fops:
-	fops_put(&kvm_gmem_fops);
-err_gmem:
-	kfree(f);
 err_fd:
 	put_unused_fd(fd);
 	return err;
-- 
2.56.0.257.gf7497c7d27-goog