/**
 * @file oprofilefs.c
 *
 * @remark Copyright 2002 OProfile authors
 * @remark Read the file COPYING
 *
 * @author John Levon
 *
 * A simple filesystem for configuration and
 * access of oprofile.
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/oprofile.h>
#include <linux/fs.h>
#include <linux/fs_context.h>
#include <linux/pagemap.h>
#include <linux/uaccess.h>

#include "oprof.h"

#define OPROFILEFS_MAGIC 0x6f70726f

DEFINE_RAW_SPINLOCK(oprofilefs_lock);

static struct inode *oprofilefs_get_inode(struct super_block *sb, int mode)
{
        struct inode *inode = new_inode(sb);

        if (inode) {
                inode->i_ino = get_next_ino();
                inode->i_mode = mode;
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
        }
        return inode;
}


static const struct super_operations s_ops = {
        .statfs         = simple_statfs,
        .drop_inode     = generic_delete_inode,
};


ssize_t oprofilefs_str_to_user(char const *str, char __user *buf, size_t count, loff_t *offset)
{
        return simple_read_from_buffer(buf, count, offset, str, strlen(str));
}


#define TMPBUFSIZE 50

ssize_t oprofilefs_ulong_to_user(unsigned long val, char __user *buf, size_t count, loff_t *offset)
{
        char tmpbuf[TMPBUFSIZE];
        size_t maxlen = snprintf(tmpbuf, TMPBUFSIZE, "%lu\n", val);
        if (maxlen > TMPBUFSIZE)
                maxlen = TMPBUFSIZE;
        return simple_read_from_buffer(buf, count, offset, tmpbuf, maxlen);
}


/*
 * Note: If oprofilefs_ulong_from_user() returns 0, then *val remains
 * unchanged and might be uninitialized. This follows write syscall
 * implementation when count is zero: "If count is zero ... [and if]
 * no errors are detected, 0 will be returned without causing any
 * other effect." (man 2 write)
 */
int oprofilefs_ulong_from_user(unsigned long *val, char const __user *buf, size_t count)
{
        char tmpbuf[TMPBUFSIZE];
        unsigned long flags;

        if (!count)
                return 0;

        if (count > TMPBUFSIZE - 1)
                return -EINVAL;

        memset(tmpbuf, 0x0, TMPBUFSIZE);

        if (copy_from_user(tmpbuf, buf, count))
                return -EFAULT;

        raw_spin_lock_irqsave(&oprofilefs_lock, flags);
        *val = simple_strtoul(tmpbuf, NULL, 0);
        raw_spin_unlock_irqrestore(&oprofilefs_lock, flags);
        return count;
}


static ssize_t ulong_read_file(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
        unsigned long *val = file->private_data;
        return oprofilefs_ulong_to_user(*val, buf, count, offset);
}


static ssize_t ulong_write_file(struct file *file, char const __user *buf, size_t count, loff_t *offset)
{
        unsigned long value;
        int retval;

        if (*offset)
                return -EINVAL;

        retval = oprofilefs_ulong_from_user(&value, buf, count);
        if (retval <= 0)
                return retval;

        retval = oprofile_set_ulong(file->private_data, value);
        if (retval)
                return retval;

        return count;
}


static const struct file_operations ulong_fops = {
        .read           = ulong_read_file,
        .write          = ulong_write_file,
        .open           = simple_open,
        .llseek         = default_llseek,
};


static const struct file_operations ulong_ro_fops = {
        .read           = ulong_read_file,
        .open           = simple_open,
        .llseek         = default_llseek,
};


static int __oprofilefs_create_file(struct dentry *root, char const *name,
        const struct file_operations *fops, int perm, void *priv)
{
        struct dentry *dentry;
        struct inode *inode;

        if (!root)
                return -ENOMEM;

        inode_lock(d_inode(root));
        dentry = d_alloc_name(root, name);
        if (!dentry) {
                inode_unlock(d_inode(root));
                return -ENOMEM;
        }
        inode = oprofilefs_get_inode(root->d_sb, S_IFREG | perm);
        if (!inode) {
                dput(dentry);
                inode_unlock(d_inode(root));
                return -ENOMEM;
        }
        inode->i_fop = fops;
        inode->i_private = priv;
        d_add(dentry, inode);
        inode_unlock(d_inode(root));
        return 0;
}


int oprofilefs_create_ulong(struct dentry *root,
        char const *name, unsigned long *val)
{
        return __oprofilefs_create_file(root, name,
                                        &ulong_fops, 0644, val);
}


int oprofilefs_create_ro_ulong(struct dentry *root,
        char const *name, unsigned long *val)
{
        return __oprofilefs_create_file(root, name,
                                        &ulong_ro_fops, 0444, val);
}


static ssize_t atomic_read_file(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
        atomic_t *val = file->private_data;
        return oprofilefs_ulong_to_user(atomic_read(val), buf, count, offset);
}


static const struct file_operations atomic_ro_fops = {
        .read           = atomic_read_file,
        .open           = simple_open,
        .llseek         = default_llseek,
};


int oprofilefs_create_ro_atomic(struct dentry *root,
        char const *name, atomic_t *val)
{
        return __oprofilefs_create_file(root, name,
                                        &atomic_ro_fops, 0444, val);
}


int oprofilefs_create_file(struct dentry *root,
        char const *name, const struct file_operations *fops)
{
        return __oprofilefs_create_file(root, name, fops, 0644, NULL);
}


int oprofilefs_create_file_perm(struct dentry *root,
        char const *name, const struct file_operations *fops, int perm)
{
        return __oprofilefs_create_file(root, name, fops, perm, NULL);
}


struct dentry *oprofilefs_mkdir(struct dentry *parent, char const *name)
{
        struct dentry *dentry;
        struct inode *inode;

        inode_lock(d_inode(parent));
        dentry = d_alloc_name(parent, name);
        if (!dentry) {
                inode_unlock(d_inode(parent));
                return NULL;
        }
        inode = oprofilefs_get_inode(parent->d_sb, S_IFDIR | 0755);
        if (!inode) {
                dput(dentry);
                inode_unlock(d_inode(parent));
                return NULL;
        }
        inode->i_op = &simple_dir_inode_operations;
        inode->i_fop = &simple_dir_operations;
        d_add(dentry, inode);
        inode_unlock(d_inode(parent));
        return dentry;
}


static int oprofilefs_fill_super(struct super_block *sb, struct fs_context *fc)
{
        struct inode *root_inode;

        sb->s_blocksize = PAGE_SIZE;
        sb->s_blocksize_bits = PAGE_SHIFT;
        sb->s_magic = OPROFILEFS_MAGIC;
        sb->s_op = &s_ops;
        sb->s_time_gran = 1;

        root_inode = oprofilefs_get_inode(sb, S_IFDIR | 0755);
        if (!root_inode)
                return -ENOMEM;
        root_inode->i_op = &simple_dir_inode_operations;
        root_inode->i_fop = &simple_dir_operations;
        sb->s_root = d_make_root(root_inode);
        if (!sb->s_root)
                return -ENOMEM;

        oprofile_create_files(sb->s_root);

        // FIXME: verify kill_litter_super removes our dentries
        return 0;
}

static int oprofilefs_get_tree(struct fs_context *fc)
{
        return get_tree_single(fc, oprofilefs_fill_super);
}

static const struct fs_context_operations oprofilefs_context_ops = {
        .get_tree       = oprofilefs_get_tree,
};

static int oprofilefs_init_fs_context(struct fs_context *fc)
{
        fc->ops = &oprofilefs_context_ops;
        return 0;
}

static struct file_system_type oprofilefs_type = {
        .owner          = THIS_MODULE,
        .name           = "oprofilefs",
        .init_fs_context = oprofilefs_init_fs_context,
        .kill_sb        = kill_litter_super,
};
MODULE_ALIAS_FS("oprofilefs");


int __init oprofilefs_register(void)
{
        return register_filesystem(&oprofilefs_type);
}


void __exit oprofilefs_unregister(void)
{
        unregister_filesystem(&oprofilefs_type);
}