On Mon, 12 Jun 2006 14:28:32 +0200
Miklos Szeredi <[email protected]> wrote:
> Add a control filesystem to fuse, replacing the attributes currently
> exported through sysfs. An empty directory '/sys/fs/fuse/connections'
> is still created in sysfs, and mounting the control filesystem here
> provides backward compatibility.
>
> Advantages of the control filesystem over the previous solution:
>
> - allows the object directory and the attributes to be owned by the
> filesystem owner, hence letting unpriviled users abort the
> filesystem connection
>
> - does not suffer from module unload race
>
Presumably people with currently-working setups will find that whatever
they used to have in /sys/fs/fuse/connections won't be there any more, so
this is a non-back-compatible change. How do we help them with that?
> +static ssize_t fuse_conn_waiting_read(struct file *file, char __user *buf,
> + size_t len, loff_t *ppos)
> +{
> + char tmp[32];
> + size_t size;
> +
> + if (!*ppos) {
> + struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
> + if (!fc)
> + return 0;
> +
> + file->private_data = (void *) atomic_read(&fc->num_waiting);
> + fuse_conn_put(fc);
> + }
> + size = sprintf(tmp, "%i\n", (int) file->private_data);
> + return simple_read_from_buffer(buf, len, ppos, tmp, size);
> +}
What happens if the first read isn't at file offset 0?
> +
> +static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
> + struct fuse_conn *fc,
> + const char *name,
> + int mode, int nlink,
> + struct inode_operations *iop,
> + const struct file_operations *fop)
> +{
> + struct dentry *dentry;
> + struct inode *inode;
> +
> + BUG_ON(fc->ctl_ndents >= FUSE_CTL_NUM_DENTRIES);
> + dentry = d_alloc_name(parent, name);
> + if (!dentry)
> + return NULL;
> +
> + fc->ctl_dentry[fc->ctl_ndents++] = dentry;
What locking protects fc->ctl_ndents?
> + inode = new_inode(fuse_control_sb);
> + if (!inode)
> + return NULL;
> +
> + inode->i_mode = mode;
> + inode->i_uid = fc->user_id;
> + inode->i_gid = fc->group_id;
> + inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
> + if (iop)
> + inode->i_op = iop;
Is iop ever null?
> + inode->i_fop = fop;
> + inode->i_nlink = nlink;
> + inode->u.generic_ip = fc;
> + d_add(dentry, inode);
> + return dentry;
> +}
> +
> +int fuse_ctl_add_conn(struct fuse_conn *fc)
> +{
> + struct dentry *parent;
> + char name[32];
> +
> + if (!fuse_control_sb)
> + return 0;
Can this happen?
> + parent = fuse_control_sb->s_root;
> + parent->d_inode->i_nlink++;
What locking protects i_nlink?
> + sprintf(name, "%llu", (unsigned long long) fc->id);
> + parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
> + &simple_dir_inode_operations,
> + &simple_dir_operations);
> + if (!parent)
> + goto err;
> +
> + if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
> + NULL, &fuse_ctl_waiting_ops) ||
> + !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
> + NULL, &fuse_ctl_abort_ops))
> + goto err;
> +
> + return 0;
> +
> + err:
> + fuse_ctl_remove_conn(fc);
> + return -ENOMEM;
> +}
> +
> +void fuse_ctl_remove_conn(struct fuse_conn *fc)
> +{
> + int i;
> +
> + if (!fuse_control_sb)
> + return;
> +
> + for (i = fc->ctl_ndents - 1; i >= 0; i--) {
> + struct dentry *dentry = fc->ctl_dentry[i];
> + dentry->d_inode->u.generic_ip = NULL;
> + d_drop(dentry);
> + dput(dentry);
> + }
> + fuse_control_sb->s_root->d_inode->i_nlink--;
Ditto.
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