Re: [PATCH v2 3/9] mm/mshare: make msharefs writable and support directories

Darrick J. Wong
2022-06-30T21:34:41Z

On Wed, Jun 29, 2022 at 04:53:54PM -0600, Khalid Aziz wrote:
> Make msharefs filesystem writable and allow creating directories
> to support better access control to mshare'd regions defined in
> msharefs.
>
> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
> ---
> mm/mshare.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 186 insertions(+), 9 deletions(-)
>
> diff --git a/mm/mshare.c b/mm/mshare.c
> index 3e448e11c742..2d5924d39221 100644
> --- a/mm/mshare.c
> +++ b/mm/mshare.c
> @@ -21,11 +21,21 @@
> #include <linux/fileattr.h>
> #include <uapi/linux/magic.h>
> #include <uapi/linux/limits.h>
> +#include <uapi/linux/mman.h>
>
> static struct super_block *msharefs_sb;
>
> +static const struct inode_operations msharefs_dir_inode_ops;
> +static const struct inode_operations msharefs_file_inode_ops;
> +
> +static int
> +msharefs_open(struct inode *inode, struct file *file)
> +{
> + return simple_open(inode, file);
> +}
> +
> static const struct file_operations msharefs_file_operations = {
> - .open = simple_open,
> + .open = msharefs_open,
> .llseek = no_llseek,
> };
>
> @@ -42,6 +52,113 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
> return 0;
> }
>
> +static struct dentry
> +*msharefs_alloc_dentry(struct dentry *parent, const char *name)
> +{
> + struct dentry *d;
> + struct qstr q;
> + int err;
> +
> + q.name = name;
> + q.len = strlen(name);
> +
> + err = msharefs_d_hash(parent, &q);
> + if (err)
> + return ERR_PTR(err);
> +
> + d = d_alloc(parent, &q);
> + if (d)
> + return d;
> +
> + return ERR_PTR(-ENOMEM);
> +}
> +
> +static struct inode
> +*msharefs_get_inode(struct super_block *sb, const struct inode *dir,
> + umode_t mode)
> +{
> + struct inode *inode = new_inode(sb);
> +
> + if (inode) {

Not sure why you wouldn't go with the less-indently version:

if (!inode)
return ERR_PTR(-ENOMEM);

inode->i_ino = get_next_ino();
<etc>

> + inode->i_ino = get_next_ino();
> + inode_init_owner(&init_user_ns, inode, dir, mode);
> +
> + inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
> +
> + switch (mode & S_IFMT) {

Shouldn't we set the mode somewhere?

> + case S_IFREG:
> + inode->i_op = &msharefs_file_inode_ops;
> + inode->i_fop = &msharefs_file_operations;
> + break;
> + case S_IFDIR:
> + inode->i_op = &msharefs_dir_inode_ops;
> + inode->i_fop = &simple_dir_operations;
> + inc_nlink(inode);
> + break;
> + case S_IFLNK:
> + inode->i_op = &page_symlink_inode_operations;
> + break;
> + default:
> + discard_new_inode(inode);
> + inode = NULL;
> + break;
> + }
> + }
> +
> + return inode;
> +}
> +
> +static int
> +msharefs_mknod(struct user_namespace *mnt_userns, struct inode *dir,
> + struct dentry *dentry, umode_t mode, dev_t dev)
> +{
> + struct inode *inode;
> + int err = 0;
> +
> + inode = msharefs_get_inode(dir->i_sb, dir, mode);
> + if (IS_ERR(inode))
> + return PTR_ERR(inode);

...and if @inode is NULL?

> +
> + d_instantiate(dentry, inode);
> + dget(dentry);
> + dir->i_mtime = dir->i_ctime = current_time(dir);
> +
> + return err;
> +}
> +
> +static int
> +msharefs_create(struct user_namespace *mnt_userns, struct inode *dir,
> + struct dentry *dentry, umode_t mode, bool excl)
> +{
> + return msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0);
> +}
> +
> +static int
> +msharefs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
> + struct dentry *dentry, umode_t mode)
> +{
> + int ret = msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0);
> +
> + if (!ret)
> + inc_nlink(dir);
> + return ret;
> +}
> +
> +static const struct inode_operations msharefs_file_inode_ops = {
> + .setattr = simple_setattr,
> + .getattr = simple_getattr,
> +};
> +static const struct inode_operations msharefs_dir_inode_ops = {
> + .create = msharefs_create,
> + .lookup = simple_lookup,
> + .link = simple_link,
> + .unlink = simple_unlink,
> + .mkdir = msharefs_mkdir,
> + .rmdir = simple_rmdir,
> + .mknod = msharefs_mknod,
> + .rename = simple_rename,
> +};
> +
> static void
> mshare_evict_inode(struct inode *inode)
> {
> @@ -58,7 +175,7 @@ mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
> {
> char s[80];
>
> - sprintf(s, "%ld", PGDIR_SIZE);
> + sprintf(s, "%ld\n", PGDIR_SIZE);

Changing this already?

> return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
> }
>
> @@ -72,6 +189,38 @@ static const struct super_operations mshare_s_ops = {
> .evict_inode = mshare_evict_inode,
> };
>
> +static int
> +prepopulate_files(struct super_block *s, struct inode *dir,
> + struct dentry *root, const struct tree_descr *files)
> +{
> + int i;
> + struct inode *inode;
> + struct dentry *dentry;
> +
> + for (i = 0; !files->name || files->name[0]; i++, files++) {
> + if (!files->name)
> + continue;

What ends the array? NULL name or empty name?
Do we have to erase all of these when the fs gets unmounted?

--D

> +
> + dentry = msharefs_alloc_dentry(root, files->name);
> + if (!dentry)
> + return -ENOMEM;
> +
> + inode = msharefs_get_inode(s, dir, S_IFREG | files->mode);
> + if (!inode) {
> + dput(dentry);
> + return -ENOMEM;
> + }
> + inode->i_mode = S_IFREG | files->mode;
> + inode->i_atime = inode->i_mtime = inode->i_ctime
> + = current_time(inode);
> + inode->i_fop = files->ops;
> + inode->i_ino = i;
> + d_add(dentry, inode);
> + }
> +
> + return 0;
> +}
> +
> static int
> msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
> {
> @@ -79,21 +228,49 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
> [2] = { "mshare_info", &mshare_info_ops, 0444},
> {""},
> };
> - int err;
> + struct inode *inode;
> + struct dentry *root;
> + int err = 0;
>
> - err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
> - if (!err) {
> - msharefs_sb = sb;
> - sb->s_d_op = &msharefs_d_ops;
> - sb->s_op = &mshare_s_ops;
> + sb->s_blocksize = PAGE_SIZE;
> + sb->s_blocksize_bits = PAGE_SHIFT;
> + sb->s_magic = MSHARE_MAGIC;
> + sb->s_op = &mshare_s_ops;
> + sb->s_d_op = &msharefs_d_ops;
> + sb->s_time_gran = 1;
> +
> + inode = msharefs_get_inode(sb, NULL, S_IFDIR | 0777);
> + if (!inode) {
> + err = -ENOMEM;
> + goto out;
> }
> + inode->i_ino = 1;
> + root = d_make_root(inode);
> + if (!root) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + err = prepopulate_files(sb, inode, root, mshare_files);
> + if (err < 0)
> + goto clean_root;
> +
> + sb->s_root = root;
> + msharefs_sb = sb;
> + return err;
> +
> +clean_root:
> + d_genocide(root);
> + shrink_dcache_parent(root);
> + dput(root);
> +out:
> return err;
> }
>
> static int
> msharefs_get_tree(struct fs_context *fc)
> {
> - return get_tree_single(fc, msharefs_fill_super);
> + return get_tree_nodev(fc, msharefs_fill_super);
> }
>
> static const struct fs_context_operations msharefs_context_ops = {
> --
> 2.32.0
>