drivers/xen/xenfs/super.c

   1 /*
   2  *  xenfs.c - a filesystem for passing info between the a domain and
   3  *  the hypervisor.
   4  *
   5  * 2008-10-07  Alex Zeffertt    Replaced /proc/xen/xenbus with xenfs filesystem
   6  *                              and /proc/xen compatibility mount point.
   7  *                              Turned xenfs into a loadable module.
   8  */
   9
  10 #include <linux/kernel.h>
  11 #include <linux/errno.h>
  12 #include <linux/module.h>
  13 #include <linux/fs.h>
  14 #include <linux/magic.h>
  15 #include <linux/mm.h>
  16 #include <linux/backing-dev.h>
  17
  18 #include <xen/xen.h>
  19
  20 #include "xenfs.h"
  21
  22 #include <asm/xen/hypervisor.h>
  23
  24 MODULE_DESCRIPTION("Xen filesystem");
  25 MODULE_LICENSE("GPL");
  26
  27 static int xenfs_set_page_dirty(struct page *page)
  28 {
  29         return !TestSetPageDirty(page);
  30 }
  31
  32 static const struct address_space_operations xenfs_aops = {
  33         .set_page_dirty = xenfs_set_page_dirty,
  34 };
  35
  36 static struct backing_dev_info xenfs_backing_dev_info = {
  37         .ra_pages       = 0,    /* No readahead */
  38         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  39 };
  40
  41 static struct inode *xenfs_make_inode(struct super_block *sb, int mode)
  42 {
  43         struct inode *ret = new_inode(sb);
  44
  45         if (ret) {
  46                 ret->i_mode = mode;
  47                 ret->i_mapping->a_ops = &xenfs_aops;
  48                 ret->i_mapping->backing_dev_info = &xenfs_backing_dev_info;
  49                 ret->i_uid = ret->i_gid = 0;
  50                 ret->i_blocks = 0;
  51                 ret->i_atime = ret->i_mtime = ret->i_ctime = CURRENT_TIME;
  52         }
  53         return ret;
  54 }
  55
  56 static struct dentry *xenfs_create_file(struct super_block *sb,
  57                                         struct dentry *parent,
  58                                         const char *name,
  59                                         const struct file_operations *fops,
  60                                         void *data,
  61                                         int mode)
  62 {
  63         struct dentry *dentry;
  64         struct inode *inode;
  65
  66         dentry = d_alloc_name(parent, name);
  67         if (!dentry)
  68                 return NULL;
  69
  70         inode = xenfs_make_inode(sb, S_IFREG | mode);
  71         if (!inode) {
  72                 dput(dentry);
  73                 return NULL;
  74         }
  75
  76         inode->i_fop = fops;
  77         inode->i_private = data;
  78
  79         d_add(dentry, inode);
  80         return dentry;
  81 }
  82
  83 static ssize_t capabilities_read(struct file *file, char __user *buf,
  84                                  size_t size, loff_t *off)
  85 {
  86         char *tmp = "";
  87
  88         if (xen_initial_domain())
  89                 tmp = "control_d\n";
  90
  91         return simple_read_from_buffer(buf, size, off, tmp, strlen(tmp));
  92 }
  93
  94 static const struct file_operations capabilities_file_ops = {
  95         .read = capabilities_read,
  96         .llseek = default_llseek,
  97 };
  98
  99 static int xenfs_fill_super(struct super_block *sb, void *data, int silent)
 100 {
 101         static struct tree_descr xenfs_files[] = {
 102                 [1] = {},
 103                 { "xenbus", &xenbus_file_ops, S_IRUSR|S_IWUSR },
 104                 { "capabilities", &capabilities_file_ops, S_IRUGO },
 105                 { "privcmd", &privcmd_file_ops, S_IRUSR|S_IWUSR },
 106                 {""},
 107         };
 108         int rc;
 109
 110         rc = simple_fill_super(sb, XENFS_SUPER_MAGIC, xenfs_files);
 111         if (rc < 0)
 112                 return rc;
 113
 114         if (xen_initial_domain()) {
 115                 xenfs_create_file(sb, sb->s_root, "xsd_kva",
 116                                   &xsd_kva_file_ops, NULL, S_IRUSR|S_IWUSR);
 117                 xenfs_create_file(sb, sb->s_root, "xsd_port",
 118                                   &xsd_port_file_ops, NULL, S_IRUSR|S_IWUSR);
 119         }
 120
 121         return rc;
 122 }
 123
 124 static int xenfs_mount(struct file_system_type *fs_type,
 125                         int flags, const char *dev_name,
 126                         void *data)
 127 {
 128         return mount_single(fs_type, flags, data, xenfs_fill_super);
 129 }
 130
 131 static struct file_system_type xenfs_type = {
 132         .owner =        THIS_MODULE,
 133         .name =         "xenfs",
 134         .mount =        xenfs_mount,
 135         .kill_sb =      kill_litter_super,
 136 };
 137
 138 static int __init xenfs_init(void)
 139 {
 140         int err;
 141         if (!xen_domain()) {
 142                 printk(KERN_INFO "xenfs: not registering filesystem on non-xen platform\n");
 143                 return 0;
 144         }
 145
 146         err = register_filesystem(&xenfs_type);
 147         if (err) {
 148                 printk(KERN_ERR "xenfs: Unable to register filesystem!\n");
 149                 goto out;
 150         }
 151
 152         err = bdi_init(&xenfs_backing_dev_info);
 153         if (err)
 154                 unregister_filesystem(&xenfs_type);
 155
 156  out:
 157
 158         return err;
 159 }
 160
 161 static void __exit xenfs_exit(void)
 162 {
 163         if (xen_domain())
 164                 unregister_filesystem(&xenfs_type);
 165 }
 166
 167 module_init(xenfs_init);
 168 module_exit(xenfs_exit);
 169