FIFO
fifoはmodeフラグ=S_IFIFOでmknodシステムコールが呼ばれ、user_path_create()でFIFOファイルを作成し、inodeコールバック関数dir->i_op->mknodがコールされます。
FMODE_READの時read_pipefifo_fops、FMODE_WRITEの時write_pipefifo_fops、FMODE_READ | FMODE_WRITEの時rdwr_pipefifo_fopsとなります。従ってFIFOはpipeそのものと言うことで、名前つきpipeと言われる所以です。
SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
unsigned, dev)
{
struct dentry *dentry;
struct path path;
int error;
if (S_ISDIR(mode))
return -EPERM;
dentry = user_path_create(dfd, filename, &path, 0);
if (IS_ERR(dentry))
return PTR_ERR(dentry);
if (!IS_POSIXACL(path.dentry->d_inode))
mode &= ~current_umask();
error = may_mknod(mode);
if (error)
goto out_dput;
error = mnt_want_write(path.mnt);
if (error)
goto out_dput;
error = security_path_mknod(&path, dentry, mode, dev);
if (error)
goto out_drop_write;
switch (mode & S_IFMT) {
case 0: case S_IFREG:
error = vfs_create(path.dentry->d_inode,dentry,mode,NULL);
break;
case S_IFCHR: case S_IFBLK:
error = vfs_mknod(path.dentry->d_inode,dentry,mode,
new_decode_dev(dev));
break;
case S_IFIFO: case S_IFSOCK:
error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
break;
}
out_drop_write:
mnt_drop_write(path.mnt);
out_dput:
dput(dentry);
mutex_unlock(&path.dentry->d_inode->i_mutex);
path_put(&path);
return error;
}
int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
int error = may_create(dir, dentry);
if (error)
return error;
if ((S_ISCHR(mode) || S_ISBLK(mode)) &&
!ns_capable(inode_userns(dir), CAP_MKNOD))
return -EPERM;
if (!dir->i_op->mknod)
return -EPERM;
error = devcgroup_inode_mknod(mode, dev);
if (error)
return error;
error = security_inode_mknod(dir, dentry, mode, dev);
if (error)
return error;
error = dir->i_op->mknod(dir, dentry, mode, dev);
if (!error)
fsnotify_create(dir, dentry);
return error;
}
ramfsのmknodコールバック関数です。ramfs_get_inode()でinodeを取得しますが、FIFOの時init_special_inode()がコールされ、def_fifo_fopsがinodeコールバックオペレーションに設定されます。inodeコールバック関数は、ファイルopen時FILEオペレーションコールバックとなります。
static int
ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
int error = -ENOSPC;
if (inode) {
d_instantiate(dentry, inode);
dget(dentry); /* Extra count - pin the dentry in core */
error = 0;
dir->i_mtime = dir->i_ctime = CURRENT_TIME;
}
return error;
}
struct inode *ramfs_get_inode(struct super_block *sb,
const struct inode *dir, umode_t mode, dev_t dev)
{
struct inode * inode = new_inode(sb);
if (inode) {
inode->i_ino = get_next_ino();
inode_init_owner(inode, dir, mode);
inode->i_mapping->a_ops = &ramfs_aops;
inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
mapping_set_unevictable(inode->i_mapping);
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
break;
case S_IFREG:
inode->i_op = &ramfs_file_inode_operations;
inode->i_fop = &ramfs_file_operations;
break;
case S_IFDIR:
inode->i_op = &ramfs_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
/* directory inodes start off with i_nlink == 2 (for "." entry) */
inc_nlink(inode);
break;
case S_IFLNK:
inode->i_op = &page_symlink_inode_operations;
break;
}
}
return inode;
}
void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
inode->i_mode = mode;
if (S_ISCHR(mode)) {
inode->i_fop = &def_chr_fops;
inode->i_rdev = rdev;
} else if (S_ISBLK(mode)) {
inode->i_fop = &def_blk_fops;
inode->i_rdev = rdev;
} else if (S_ISFIFO(mode))
inode->i_fop = &def_fifo_fops;
else if (S_ISSOCK(mode))
inode->i_fop = &bad_sock_fops;
else
printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o) for"
" inode %s:%lu\n", mode, inode->i_sb->s_id,
inode->i_ino);
}
def_fifo_fopsは.open/.llseekのみ有するコールバックです。読み書き用のコールバックは？ 読み書き用のコールバックはファイルopen時、.openコールバックで再設定します。これはFIFOファイルopen時の属性によって処理内容が異なるからです。FMODE_READの時read_pipefifo_fops、FMODE_WRITEの時write_pipefifo_fops、FMODE_READ | FMODE_WRITEの時rdwr_pipefifo_fopsとなります。従ってFIFOはpipeそのものと言うことで、名前つきpipeと言われる所以です。
const struct file_operations def_fifo_fops = {
.open = fifo_open, /* will set read_ or write_pipefifo_fops */
.llseek = noop_llseek,
}
static int fifo_open(struct inode *inode, struct file *filp)
{
struct pipe_inode_info *pipe;
int ret;
mutex_lock(&inode->i_mutex);
pipe = inode->i_pipe;
if (!pipe) {
ret = -ENOMEM;
pipe = alloc_pipe_info(inode);
if (!pipe)
goto err_nocleanup;
inode->i_pipe = pipe;
}
filp->f_version = 0;
filp->f_mode &= (FMODE_READ | FMODE_WRITE);
switch (filp->f_mode) {
case FMODE_READ:
filp->f_op = &read_pipefifo_fops;
pipe->r_counter++;
if (pipe->readers++ == 0)
wake_up_partner(inode);
if (!pipe->writers) {
if ((filp->f_flags & O_NONBLOCK)) {
/* suppress POLLHUP until we have
* seen a writer */
filp->f_version = pipe->w_counter;
} else {
wait_for_partner(inode, &pipe->w_counter);
if(signal_pending(current))
goto err_rd;
}
}
break;
case FMODE_WRITE:
ret = -ENXIO;
if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
goto err;
filp->f_op = &write_pipefifo_fops;
pipe->w_counter++;
if (!pipe->writers++)
wake_up_partner(inode);
if (!pipe->readers) {
wait_for_partner(inode, &pipe->r_counter);
if (signal_pending(current))
goto err_wr;
}
break;
case FMODE_READ | FMODE_WRITE:
filp->f_op = &rdwr_pipefifo_fops;
pipe->readers++;
pipe->writers++;
pipe->r_counter++;
pipe->w_counter++;
if (pipe->readers == 1 || pipe->writers == 1)
wake_up_partner(inode);
break;
default:
ret = -EINVAL;
goto err;
}
mutex_unlock(&inode->i_mutex);
return 0;
err_rd:
if (!--pipe->readers)
wake_up_interruptible(&pipe->wait);
ret = -ERESTARTSYS;
goto err;
err_wr:
if (!--pipe->writers)
wake_up_interruptible(&pipe->wait);
ret = -ERESTARTSYS;
goto err;
err:
if (!pipe->readers && !pipe->writers)
free_pipe_info(inode);
err_nocleanup:
mutex_unlock(&inode->i_mutex);
return ret;
}
loff_t noop_llseek(struct file *file, loff_t offset, int origin)
{
return file->f_pos;
}
