上个月给文件系统添加额外的属性设置接口，但却是完全脱离文件系统实现的，直接使用rpc连接元数据服务器来设置/获取属性，而没有通过文件系统的客户端。当时想着还有一种方法就是在fuse-2.8中支持了ioctl接口，可通过为分布式文件系统实现ioctl接口实现扩展属性的获取与设置。
使用ioctl首先要理解ioctl命令的封装格式，ioctl的命令对应一个32bits的整数，其格式如下：
|
2位，访问模式 |
14位，参数的大小 |
8位，魔数 |
8位序号 |
/usr/include/asm-generic/ioctl.h中提供了一系列操作ioctl命令的宏：
|
/* ioctl command encoding: 32 bits total, command in lower 16 bits,
* size of the parameter structure in the lower 14 bits of the
* upper 16 bits.
* Encoding the size of the parameter structure in the ioctl request
* is useful for catching programs compiled with old versions
* and to avoid overwriting user space outside the user buffer area.
* The highest 2 bits are reserved for indicating the ``access mode''.
* NOTE: This limits the max parameter size to 16kB -1 !
*/
/*
* The following is for compatibility across the various Linux
* platforms. The generic ioctl numbering scheme doesn't really enforce
* a type field. De facto, however, the top 8 bits of the lower 16
* bits are indeed used as a type field, so we might just as well make
* this explicit here. Please be sure to use the decoding macros
* below from now on.
*/
#define _IOC_NRBITS 8
#define _IOC_TYPEBITS 8
#define _IOC_SIZEBITS 14
#define _IOC_DIRBITS 2
#define _IOC_NRMASK ((1 << _IOC_NRBITS)-1)
#define _IOC_TYPEMASK ((1 << _IOC_TYPEBITS)-1)
#define _IOC_SIZEMASK ((1 << _IOC_SIZEBITS)-1)
#define _IOC_DIRMASK ((1 << _IOC_DIRBITS)-1)
#define _IOC_NRSHIFT 0
#define _IOC_TYPESHIFT (_IOC_NRSHIFT+_IOC_NRBITS)
#define _IOC_SIZESHIFT (_IOC_TYPESHIFT+_IOC_TYPEBITS)
#define _IOC_DIRSHIFT (_IOC_SIZESHIFT+_IOC_SIZEBITS)
/*
* Direction bits.
*/
#define _IOC_NONE 0U
#define _IOC_WRITE 1U
#define _IOC_READ 2U
#define _IOC(dir,type,nr,size) \
(((dir) << _IOC_DIRSHIFT) | \
((type) << _IOC_TYPESHIFT) | \
((nr) << _IOC_NRSHIFT) | \
((size) << _IOC_SIZESHIFT))
/* provoke compile error for invalid uses of size argument */
extern unsigned int __invalid_size_argument_for_IOC;
#define _IOC_TYPECHECK(t) \
((sizeof(t) == sizeof(t[1]) && \
sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
sizeof(t) : __invalid_size_argument_for_IOC)
/* used to create numbers */
#define _IO(type,nr) _IOC(_IOC_NONE,(type),(nr),0)
#define _IOR(type,nr,size) _IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOW(type,nr,size) _IOC(_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOWR(type,nr,size) _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOR_BAD(type,nr,size) _IOC(_IOC_READ,(type),(nr),sizeof(size))
#define _IOW_BAD(type,nr,size) _IOC(_IOC_WRITE,(type),(nr),sizeof(size))
#define _IOWR_BAD(type,nr,size) _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),sizeof(size))
/* used to decode ioctl numbers.. */
#define _IOC_DIR(nr) (((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK)
#define _IOC_TYPE(nr) (((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)
#define _IOC_NR(nr) (((nr) >> _IOC_NRSHIFT) & _IOC_NRMASK)
#define _IOC_SIZE(nr) (((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)
/* ...and for the drivers/sound files... */
#define IOC_IN (_IOC_WRITE << _IOC_DIRSHIFT)
#define IOC_OUT (_IOC_READ << _IOC_DIRSHIFT)
#define IOC_INOUT ((_IOC_WRITE|_IOC_READ) << _IOC_DIRSHIFT)
#define IOCSIZE_MASK (_IOC_SIZEMASK << _IOC_SIZESHIFT)
#define IOCSIZE_SHIFT (_IOC_SIZESHIFT)
|
在fu***mp.c中的简单的实现了ioctl接口，我系统上安装的fuse-2.7，提示fuse_operations中没有ioctl成员，这是由于fuse-2.8才引入ioctl接口，于是重新安装fuse-2.8，编译OK，但不能正常工作。
由于从fuse-2.8开始，fuse包中不再附带内核模块，内核模块已经加入到内核源代码中，而我机器上之前安装的fuse中带有内核模块，故虽然fuse的用户编程库更新到2.8版本，但运行的内核模块仍不支持ioctl接口，重启进入2.6.30.5内核，同时发现fuse-2.8.0中带了ioctl接口使用的实例（fioc.h, fioc.c, fioclient.c），运行OK。在测试自己下的例子时，发现ioctl只对文件生效，不能对目录进行操作。
怀疑是fuse对inode进行初始化时，目录的inode的i_fop结构中不含ioctl接口，读fuse内核模块的代码，验证了我的想法：
fuse_init_inode为fuse初始化inode的代码，在代码中，对于普通的文件调用了fuse_init_common，fuse_init_inode方法，最终普通文件的i_fop为fuse_file_operations；而对于目录文件，其i_fop为fuse_dir_operations，而该结构中的ioctl接口并没有被实现。
|
static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
{
inode->i_mode = attr->mode & S_IFMT;
inode->i_size = attr->size;
if (S_ISREG(inode->i_mode)) {
fuse_init_common(inode);
fuse_init_file_inode(inode);
} else if (S_ISDIR(inode->i_mode))
fuse_init_dir(inode);
else if (S_ISLNK(inode->i_mode))
fuse_init_symlink(inode);
else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
fuse_init_common(inode);
init_special_inode(inode, inode->i_mode,
new_decode_dev(attr->rdev));
} else
BUG();
}
void fuse_init_common(struct inode *inode)
{
inode->i_op = &fuse_common_inode_operations;
}
void fuse_init_file_inode(struct inode *inode)
{
inode->i_fop = &fuse_file_operations;
inode->i_data.a_ops = &fuse_file_aops;
}
void fuse_init_dir(struct inode *inode)
{
inode->i_op = &fuse_dir_inode_operations;
inode->i_fop = &fuse_dir_operations;
}
static const struct file_operations fuse_dir_operations = {
.llseek = generic_file_llseek,
.read = generic_read_dir,
.readdir = fuse_readdir,
.open = fuse_dir_open,
.release = fuse_dir_release,
.fsync = fuse_dir_fsync,
};
static const struct file_operations fuse_file_operations = {
.llseek = fuse_file_llseek,
.read = do_sync_read,
.aio_read = fuse_file_aio_read,
.write = do_sync_write,
.aio_write = fuse_file_aio_write,
.mmap = fuse_file_mmap,
.open = fuse_open,
.flush = fuse_flush,
.release = fuse_release,
.fsync = fuse_fsync,
.lock = fuse_file_lock,
.flock = fuse_file_flock,
.splice_read = generic_file_splice_read,
.unlocked_ioctl = fuse_file_ioctl,
.compat_ioctl = fuse_file_compat_ioctl,
.poll = fuse_file_poll,
};
|
fuse的ChangeLog节选：（fuse-2.8.0/ChangeLog）
2008-12-05 Miklos Szeredi <miklos@szeredi.hu>
* Implement ioctl support. On high level interface only "restricted" ioctls are supported (which are defined with the _IO(), _IOR(), _IOW() or _IOWR() macros). Unrestricted ioctls will only be allwed to CUSE (Character Device in Userspace) servers. Patch by Tejun Heo
2008-06-16 Miklos Szeredi <miklos@szeredi.hu>
* Remove fuse kernel module sources. Linux 2.6.27 will support NFS exporting.
（故要支持fuse-2.8的新特性，最好使用linux-2.6.27+的内核）
2008-05-09 Miklos Szeredi <miklos@szeredi.hu>
* Don't allow bigger than 4kB writes by default on 2.6.26 and later kernels, so that filesystems not expecting this are not broken on a kernel upgrade. Provide a 'big_writes' mount option to enable this feature. In future API revisions this may become the default.
