[RFC PATCH 13/19] KVM: guest_mem: Refactor kvm_gmem fd creation to be in layers

[Ackerley Tng]

First create a gmem inode, then create a gmem file using the inode,
then install the file into an fd.

Creating the file in layers separates inode concepts (struct kvm_gmem)
from file concepts and makes cleaning up in stages neater.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 virt/kvm/guest_mem.c | 86 +++++++++++++++++++++++++-------------------
 1 file changed, 50 insertions(+), 36 deletions(-)

diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c
index 8708139822d3..2f69ef666871 100644
--- a/virt/kvm/guest_mem.c
+++ b/virt/kvm/guest_mem.c
@@ -375,41 +375,27 @@ static const struct inode_operations kvm_gmem_iops = {
        .setattr        = kvm_gmem_setattr,
 };
 
-static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags,
-                            struct vfsmount *mnt)
+static struct inode *kvm_gmem_create_inode(struct kvm *kvm, loff_t size, u64 
flags,
+                                          struct vfsmount *mnt)
 {
+       int err;
+       struct inode *inode;
+       struct kvm_gmem *gmem;
        const char *anon_name = "[kvm-gmem]";
        const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name));
-       struct kvm_gmem *gmem;
-       struct inode *inode;
-       struct file *file;
-       int fd, err;
-
-       fd = get_unused_fd_flags(0);
-       if (fd < 0)
-               return fd;
 
        inode = alloc_anon_inode(mnt->mnt_sb);
-       if (IS_ERR(inode)) {
-               err = PTR_ERR(inode);
-               goto err_fd;
-       }
+       if (IS_ERR(inode))
+               return inode;
 
        err = security_inode_init_security_anon(inode, &qname, NULL);
        if (err)
                goto err_inode;
 
-       file = alloc_file_pseudo(inode, mnt, "kvm-gmem", O_RDWR, 
&kvm_gmem_fops);
-       if (IS_ERR(file)) {
-               err = PTR_ERR(file);
-               goto err_inode;
-       }
-
+       err = -ENOMEM;
        gmem = kzalloc(sizeof(*gmem), GFP_KERNEL);
-       if (!gmem) {
-               err = -ENOMEM;
-               goto err_file;
-       }
+       if (!gmem)
+               goto err_inode;
 
        xa_init(&gmem->bindings);
 
@@ -426,24 +412,41 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t 
size, u64 flags,
        mapping_set_large_folios(inode->i_mapping);
        mapping_set_unevictable(inode->i_mapping);
 
-       file->f_flags |= O_LARGEFILE;
-       file->f_mapping = inode->i_mapping;
-       file->private_data = gmem;
-
-       fd_install(fd, file);
-       return fd;
+       return inode;
 
-err_file:
-       fput(file);
 err_inode:
        iput(inode);
-err_fd:
-       put_unused_fd(fd);
-       return err;
+       return ERR_PTR(err);
+}
+
+
+static struct file *kvm_gmem_create_file(struct kvm *kvm, loff_t size, u64 
flags,
+                                        struct vfsmount *mnt)
+{
+       struct file *file;
+       struct inode *inode;
+
+       inode = kvm_gmem_create_inode(kvm, size, flags, mnt);
+       if (IS_ERR(inode))
+               return ERR_CAST(inode);
+
+       file = alloc_file_pseudo(inode, mnt, "kvm-gmem", O_RDWR, 
&kvm_gmem_fops);
+       if (IS_ERR(file)) {
+               iput(inode);
+               return file;
+       }
+
+       file->f_flags |= O_LARGEFILE;
+       file->f_mapping = inode->i_mapping;
+       file->private_data = inode->i_mapping->private_data;
+
+       return file;
 }
 
 int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *gmem)
 {
+       int fd;
+       struct file *file;
        loff_t size = gmem->size;
        u64 flags = gmem->flags;
 
@@ -462,7 +465,18 @@ int kvm_gmem_create(struct kvm *kvm, struct 
kvm_create_guest_memfd *gmem)
 #endif
        }
 
-       return __kvm_gmem_create(kvm, size, flags, kvm_gmem_mnt);
+       fd = get_unused_fd_flags(0);
+       if (fd < 0)
+               return fd;
+
+       file = kvm_gmem_create_file(kvm, size, flags, kvm_gmem_mnt);
+       if (IS_ERR(file)) {
+               put_unused_fd(fd);
+               return PTR_ERR(file);
+       }
+
+       fd_install(fd, file);
+       return fd;
 }
 
 int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
-- 
2.41.0.rc0.172.g3f132b7071-goog