fs/quota/quota.c - linux - Git at Google

 /*
  * Quota code necessary even when VFS quota support is not compiled
  * into the kernel.  The interesting stuff is over in dquot.c, here
  * we have symbols for initial quotactl(2) handling, the sysctl(2)
  * variables, etc - things needed even when quota support disabled.
  */

 #include <linux/fs.h>
 #include <linux/namei.h>
 #include <linux/slab.h>
 #include <asm/current.h>
 #include <asm/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/buffer_head.h>
 #include <linux/capability.h>
 #include <linux/quotaops.h>
 #include <linux/types.h>
 #include <linux/writeback.h>

 static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
 				     qid_t id)
 {
 	switch (cmd) {
 	/* these commands do not require any special privilegues */
 	case Q_GETFMT:
 	case Q_SYNC:
 	case Q_GETINFO:
 	case Q_XGETQSTAT:
 	case Q_XQUOTASYNC:
 		break;
 	/* allow to query information for dquots we "own" */
 	case Q_GETQUOTA:
 	case Q_XGETQUOTA:
 		if ((type == USRQUOTA && current_euid() == id) ||
 		    (type == GRPQUOTA && in_egroup_p(id)))
 			break;
 		/*FALLTHROUGH*/
 	default:
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
 	}

 	return security_quotactl(cmd, type, id, sb);
 }

 static int quota_sync_all(int type)
 {
 	struct super_block *sb;
 	int ret;

 	if (type >= MAXQUOTAS)
 		return -EINVAL;
 	ret = security_quotactl(Q_SYNC, type, 0, NULL);
 	if (ret)
 		return ret;

 	spin_lock(&sb_lock);
 restart:
 	list_for_each_entry(sb, &super_blocks, s_list) {
 		if (!sb->s_qcop || !sb->s_qcop->quota_sync)
 			continue;

 		sb->s_count++;
 		spin_unlock(&sb_lock);
 		down_read(&sb->s_umount);
 		if (sb->s_root)
 			sb->s_qcop->quota_sync(sb, type, 1);
 		up_read(&sb->s_umount);
 		spin_lock(&sb_lock);
 		if (__put_super_and_need_restart(sb))
 			goto restart;
 	}
 	spin_unlock(&sb_lock);

 	return 0;
 }

 static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,
 		         void __user *addr)
 {
 	char *pathname;
 	int ret = -ENOSYS;

 	pathname = getname(addr);
 	if (IS_ERR(pathname))
 		return PTR_ERR(pathname);
 	if (sb->s_qcop->quota_on)
 		ret = sb->s_qcop->quota_on(sb, type, id, pathname, 0);
 	putname(pathname);
 	return ret;
 }

 static int quota_getfmt(struct super_block *sb, int type, void __user *addr)
 {
 	__u32 fmt;

 	down_read(&sb_dqopt(sb)->dqptr_sem);
 	if (!sb_has_quota_active(sb, type)) {
 		up_read(&sb_dqopt(sb)->dqptr_sem);
 		return -ESRCH;
 	}
 	fmt = sb_dqopt(sb)->info[type].dqi_format->qf_fmt_id;
 	up_read(&sb_dqopt(sb)->dqptr_sem);
 	if (copy_to_user(addr, &fmt, sizeof(fmt)))
 		return -EFAULT;
 	return 0;
 }

 static int quota_getinfo(struct super_block *sb, int type, void __user *addr)
 {
 	struct if_dqinfo info;
 	int ret;

 	if (!sb->s_qcop->get_info)
 		return -ENOSYS;
 	ret = sb->s_qcop->get_info(sb, type, &info);
 	if (!ret && copy_to_user(addr, &info, sizeof(info)))
 		return -EFAULT;
 	return ret;
 }

 static int quota_setinfo(struct super_block *sb, int type, void __user *addr)
 {
 	struct if_dqinfo info;

 	if (copy_from_user(&info, addr, sizeof(info)))
 		return -EFAULT;
 	if (!sb->s_qcop->set_info)
 		return -ENOSYS;
 	return sb->s_qcop->set_info(sb, type, &info);
 }

 static void copy_to_if_dqblk(struct if_dqblk *dst, struct fs_disk_quota *src)
 {
 	dst->dqb_bhardlimit = src->d_blk_hardlimit;
 	dst->dqb_bsoftlimit = src->d_blk_softlimit;
 	dst->dqb_curspace = src->d_bcount;
 	dst->dqb_ihardlimit = src->d_ino_hardlimit;
 	dst->dqb_isoftlimit = src->d_ino_softlimit;
 	dst->dqb_curinodes = src->d_icount;
 	dst->dqb_btime = src->d_btimer;
 	dst->dqb_itime = src->d_itimer;
 	dst->dqb_valid = QIF_ALL;
 }

 static int quota_getquota(struct super_block *sb, int type, qid_t id,
 			  void __user *addr)
 {
 	struct fs_disk_quota fdq;
 	struct if_dqblk idq;
 	int ret;

 	if (!sb->s_qcop->get_dqblk)
 		return -ENOSYS;
 	ret = sb->s_qcop->get_dqblk(sb, type, id, &fdq);
 	if (ret)
 		return ret;
 	copy_to_if_dqblk(&idq, &fdq);
 	if (copy_to_user(addr, &idq, sizeof(idq)))
 		return -EFAULT;
 	return 0;
 }

 static void copy_from_if_dqblk(struct fs_disk_quota *dst, struct if_dqblk *src)
 {
 	dst->d_blk_hardlimit = src->dqb_bhardlimit;
 	dst->d_blk_softlimit  = src->dqb_bsoftlimit;
 	dst->d_bcount = src->dqb_curspace;
 	dst->d_ino_hardlimit = src->dqb_ihardlimit;
 	dst->d_ino_softlimit = src->dqb_isoftlimit;
 	dst->d_icount = src->dqb_curinodes;
 	dst->d_btimer = src->dqb_btime;
 	dst->d_itimer = src->dqb_itime;

 	dst->d_fieldmask = 0;
 	if (src->dqb_valid & QIF_BLIMITS)
 		dst->d_fieldmask |= FS_DQ_BSOFT | FS_DQ_BHARD;
 	if (src->dqb_valid & QIF_SPACE)
 		dst->d_fieldmask |= FS_DQ_BCOUNT;
 	if (src->dqb_valid & QIF_ILIMITS)
 		dst->d_fieldmask |= FS_DQ_ISOFT | FS_DQ_IHARD;
 	if (src->dqb_valid & QIF_INODES)
 		dst->d_fieldmask |= FS_DQ_ICOUNT;
 	if (src->dqb_valid & QIF_BTIME)
 		dst->d_fieldmask |= FS_DQ_BTIMER;
 	if (src->dqb_valid & QIF_ITIME)
 		dst->d_fieldmask |= FS_DQ_ITIMER;
 }

 static int quota_setquota(struct super_block *sb, int type, qid_t id,
 			  void __user *addr)
 {
 	struct fs_disk_quota fdq;
 	struct if_dqblk idq;

 	if (copy_from_user(&idq, addr, sizeof(idq)))
 		return -EFAULT;
 	if (!sb->s_qcop->set_dqblk)
 		return -ENOSYS;
 	copy_from_if_dqblk(&fdq, &idq);
 	return sb->s_qcop->set_dqblk(sb, type, id, &fdq);
 }

 static int quota_setxstate(struct super_block *sb, int cmd, void __user *addr)
 {
 	__u32 flags;

 	if (copy_from_user(&flags, addr, sizeof(flags)))
 		return -EFAULT;
 	if (!sb->s_qcop->set_xstate)
 		return -ENOSYS;
 	return sb->s_qcop->set_xstate(sb, flags, cmd);
 }

 static int quota_getxstate(struct super_block *sb, void __user *addr)
 {
 	struct fs_quota_stat fqs;
 	int ret;

 	if (!sb->s_qcop->get_xstate)
 		return -ENOSYS;
 	ret = sb->s_qcop->get_xstate(sb, &fqs);
 	if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
 		return -EFAULT;
 	return ret;
 }

 static int quota_setxquota(struct super_block *sb, int type, qid_t id,
 			   void __user *addr)
 {
 	struct fs_disk_quota fdq;

 	if (copy_from_user(&fdq, addr, sizeof(fdq)))
 		return -EFAULT;
 	if (!sb->s_qcop->set_dqblk)
 		return -ENOSYS;
 	return sb->s_qcop->set_dqblk(sb, type, id, &fdq);
 }

 static int quota_getxquota(struct super_block *sb, int type, qid_t id,
 			   void __user *addr)
 {
 	struct fs_disk_quota fdq;
 	int ret;

 	if (!sb->s_qcop->get_dqblk)
 		return -ENOSYS;
 	ret = sb->s_qcop->get_dqblk(sb, type, id, &fdq);
 	if (!ret && copy_to_user(addr, &fdq, sizeof(fdq)))
 		return -EFAULT;
 	return ret;
 }

 /* Copy parameters and call proper function */
 static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 		       void __user *addr)
 {
 	int ret;

 	if (type >= (XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS))
 		return -EINVAL;
 	if (!sb->s_qcop)
 		return -ENOSYS;

 	ret = check_quotactl_permission(sb, type, cmd, id);
 	if (ret < 0)
 		return ret;

 	switch (cmd) {
 	case Q_QUOTAON:
 		return quota_quotaon(sb, type, cmd, id, addr);
 	case Q_QUOTAOFF:
 		if (!sb->s_qcop->quota_off)
 			return -ENOSYS;
 		return sb->s_qcop->quota_off(sb, type, 0);
 	case Q_GETFMT:
 		return quota_getfmt(sb, type, addr);
 	case Q_GETINFO:
 		return quota_getinfo(sb, type, addr);
 	case Q_SETINFO:
 		return quota_setinfo(sb, type, addr);
 	case Q_GETQUOTA:
 		return quota_getquota(sb, type, id, addr);
 	case Q_SETQUOTA:
 		return quota_setquota(sb, type, id, addr);
 	case Q_SYNC:
 		if (!sb->s_qcop->quota_sync)
 			return -ENOSYS;
 		return sb->s_qcop->quota_sync(sb, type, 1);
 	case Q_XQUOTAON:
 	case Q_XQUOTAOFF:
 	case Q_XQUOTARM:
 		return quota_setxstate(sb, cmd, addr);
 	case Q_XGETQSTAT:
 		return quota_getxstate(sb, addr);
 	case Q_XSETQLIM:
 		return quota_setxquota(sb, type, id, addr);
 	case Q_XGETQUOTA:
 		return quota_getxquota(sb, type, id, addr);
 	case Q_XQUOTASYNC:
 		/* caller already holds s_umount */
 		if (sb->s_flags & MS_RDONLY)
 			return -EROFS;
 		writeback_inodes_sb(sb);
 		return 0;
 	default:
 		return -EINVAL;
 	}
 }

 /*
  * look up a superblock on which quota ops will be performed
  * - use the name of a block device to find the superblock thereon
  */
 static struct super_block *quotactl_block(const char __user *special)
 {
 #ifdef CONFIG_BLOCK
 	struct block_device *bdev;
 	struct super_block *sb;
 	char *tmp = getname(special);

 	if (IS_ERR(tmp))
 		return ERR_CAST(tmp);
 	bdev = lookup_bdev(tmp);
 	putname(tmp);
 	if (IS_ERR(bdev))
 		return ERR_CAST(bdev);
 	sb = get_super(bdev);
 	bdput(bdev);
 	if (!sb)
 		return ERR_PTR(-ENODEV);

 	return sb;
 #else
 	return ERR_PTR(-ENODEV);
 #endif
 }

 /*
  * This is the system call interface. This communicates with
  * the user-level programs. Currently this only supports diskquota
  * calls. Maybe we need to add the process quotas etc. in the future,
  * but we probably should use rlimits for that.
  */
 SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
 		qid_t, id, void __user *, addr)
 {
 	uint cmds, type;
 	struct super_block *sb = NULL;
 	int ret;

 	cmds = cmd >> SUBCMDSHIFT;
 	type = cmd & SUBCMDMASK;

 	/*
 	 * As a special case Q_SYNC can be called without a specific device.
 	 * It will iterate all superblocks that have quota enabled and call
 	 * the sync action on each of them.
 	 */
 	if (!special) {
 		if (cmds == Q_SYNC)
 			return quota_sync_all(type);
 		return -ENODEV;
 	}

 	sb = quotactl_block(special);
 	if (IS_ERR(sb))
 		return PTR_ERR(sb);

 	ret = do_quotactl(sb, type, cmds, id, addr);

 	drop_super(sb);
 	return ret;
 }
	/*
	* Quota code necessary even when VFS quota support is not compiled
	* into the kernel. The interesting stuff is over in dquot.c, here
	* we have symbols for initial quotactl(2) handling, the sysctl(2)
	* variables, etc - things needed even when quota support disabled.
	*/

	#include <linux/fs.h>
	#include <linux/namei.h>
	#include <linux/slab.h>
	#include <asm/current.h>
	#include <asm/uaccess.h>
	#include <linux/kernel.h>
	#include <linux/security.h>
	#include <linux/syscalls.h>
	#include <linux/buffer_head.h>
	#include <linux/capability.h>
	#include <linux/quotaops.h>
	#include <linux/types.h>
	#include <linux/writeback.h>

	static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
	qid_t id)
	{
	switch (cmd) {
	/* these commands do not require any special privilegues */
	case Q_GETFMT:
	case Q_SYNC:
	case Q_GETINFO:
	case Q_XGETQSTAT:
	case Q_XQUOTASYNC:
	break;
	/* allow to query information for dquots we "own" */
	case Q_GETQUOTA:
	case Q_XGETQUOTA:
	if ((type == USRQUOTA && current_euid() == id) \|\|
	(type == GRPQUOTA && in_egroup_p(id)))
	break;
	/FALLTHROUGH/
	default:
	if (!capable(CAP_SYS_ADMIN))
	return -EPERM;
	}

	return security_quotactl(cmd, type, id, sb);
	}

	static int quota_sync_all(int type)
	{
	struct super_block *sb;
	int ret;

	if (type >= MAXQUOTAS)
	return -EINVAL;
	ret = security_quotactl(Q_SYNC, type, 0, NULL);
	if (ret)
	return ret;

	spin_lock(&sb_lock);
	restart:
	list_for_each_entry(sb, &super_blocks, s_list) {
	if (!sb->s_qcop \|\| !sb->s_qcop->quota_sync)
	continue;

	sb->s_count++;
	spin_unlock(&sb_lock);
	down_read(&sb->s_umount);
	if (sb->s_root)
	sb->s_qcop->quota_sync(sb, type, 1);
	up_read(&sb->s_umount);
	spin_lock(&sb_lock);
	if (__put_super_and_need_restart(sb))
	goto restart;
	}
	spin_unlock(&sb_lock);

	return 0;
	}

	static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,
	void __user *addr)
	{
	char *pathname;
	int ret = -ENOSYS;

	pathname = getname(addr);
	if (IS_ERR(pathname))
	return PTR_ERR(pathname);
	if (sb->s_qcop->quota_on)
	ret = sb->s_qcop->quota_on(sb, type, id, pathname, 0);
	putname(pathname);
	return ret;
	}

	static int quota_getfmt(struct super_block sb, int type, void __user addr)
	{
	__u32 fmt;

	down_read(&sb_dqopt(sb)->dqptr_sem);
	if (!sb_has_quota_active(sb, type)) {
	up_read(&sb_dqopt(sb)->dqptr_sem);
	return -ESRCH;
	}
	fmt = sb_dqopt(sb)->info[type].dqi_format->qf_fmt_id;
	up_read(&sb_dqopt(sb)->dqptr_sem);
	if (copy_to_user(addr, &fmt, sizeof(fmt)))
	return -EFAULT;
	return 0;
	}

	static int quota_getinfo(struct super_block sb, int type, void __user addr)
	{
	struct if_dqinfo info;
	int ret;

	if (!sb->s_qcop->get_info)
	return -ENOSYS;
	ret = sb->s_qcop->get_info(sb, type, &info);
	if (!ret && copy_to_user(addr, &info, sizeof(info)))
	return -EFAULT;
	return ret;
	}

	static int quota_setinfo(struct super_block sb, int type, void __user addr)
	{
	struct if_dqinfo info;

	if (copy_from_user(&info, addr, sizeof(info)))
	return -EFAULT;
	if (!sb->s_qcop->set_info)
	return -ENOSYS;
	return sb->s_qcop->set_info(sb, type, &info);
	}

	static void copy_to_if_dqblk(struct if_dqblk dst, struct fs_disk_quota src)
	{
	dst->dqb_bhardlimit = src->d_blk_hardlimit;
	dst->dqb_bsoftlimit = src->d_blk_softlimit;
	dst->dqb_curspace = src->d_bcount;
	dst->dqb_ihardlimit = src->d_ino_hardlimit;
	dst->dqb_isoftlimit = src->d_ino_softlimit;
	dst->dqb_curinodes = src->d_icount;
	dst->dqb_btime = src->d_btimer;
	dst->dqb_itime = src->d_itimer;
	dst->dqb_valid = QIF_ALL;
	}

	static int quota_getquota(struct super_block *sb, int type, qid_t id,
	void __user *addr)
	{
	struct fs_disk_quota fdq;
	struct if_dqblk idq;
	int ret;

	if (!sb->s_qcop->get_dqblk)
	return -ENOSYS;
	ret = sb->s_qcop->get_dqblk(sb, type, id, &fdq);
	if (ret)
	return ret;
	copy_to_if_dqblk(&idq, &fdq);
	if (copy_to_user(addr, &idq, sizeof(idq)))
	return -EFAULT;
	return 0;
	}

	static void copy_from_if_dqblk(struct fs_disk_quota dst, struct if_dqblk src)
	{
	dst->d_blk_hardlimit = src->dqb_bhardlimit;
	dst->d_blk_softlimit = src->dqb_bsoftlimit;
	dst->d_bcount = src->dqb_curspace;
	dst->d_ino_hardlimit = src->dqb_ihardlimit;
	dst->d_ino_softlimit = src->dqb_isoftlimit;
	dst->d_icount = src->dqb_curinodes;
	dst->d_btimer = src->dqb_btime;
	dst->d_itimer = src->dqb_itime;

	dst->d_fieldmask = 0;
	if (src->dqb_valid & QIF_BLIMITS)
	dst->d_fieldmask \|= FS_DQ_BSOFT \| FS_DQ_BHARD;
	if (src->dqb_valid & QIF_SPACE)
	dst->d_fieldmask \|= FS_DQ_BCOUNT;
	if (src->dqb_valid & QIF_ILIMITS)
	dst->d_fieldmask \|= FS_DQ_ISOFT \| FS_DQ_IHARD;
	if (src->dqb_valid & QIF_INODES)
	dst->d_fieldmask \|= FS_DQ_ICOUNT;
	if (src->dqb_valid & QIF_BTIME)
	dst->d_fieldmask \|= FS_DQ_BTIMER;
	if (src->dqb_valid & QIF_ITIME)
	dst->d_fieldmask \|= FS_DQ_ITIMER;
	}

	static int quota_setquota(struct super_block *sb, int type, qid_t id,
	void __user *addr)
	{
	struct fs_disk_quota fdq;
	struct if_dqblk idq;

	if (copy_from_user(&idq, addr, sizeof(idq)))
	return -EFAULT;
	if (!sb->s_qcop->set_dqblk)
	return -ENOSYS;
	copy_from_if_dqblk(&fdq, &idq);
	return sb->s_qcop->set_dqblk(sb, type, id, &fdq);
	}

	static int quota_setxstate(struct super_block sb, int cmd, void __user addr)
	{
	__u32 flags;

	if (copy_from_user(&flags, addr, sizeof(flags)))
	return -EFAULT;
	if (!sb->s_qcop->set_xstate)
	return -ENOSYS;
	return sb->s_qcop->set_xstate(sb, flags, cmd);
	}

	static int quota_getxstate(struct super_block sb, void __user addr)
	{
	struct fs_quota_stat fqs;
	int ret;

	if (!sb->s_qcop->get_xstate)
	return -ENOSYS;
	ret = sb->s_qcop->get_xstate(sb, &fqs);
	if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
	return -EFAULT;
	return ret;
	}

	static int quota_setxquota(struct super_block *sb, int type, qid_t id,
	void __user *addr)
	{
	struct fs_disk_quota fdq;

	if (copy_from_user(&fdq, addr, sizeof(fdq)))
	return -EFAULT;
	if (!sb->s_qcop->set_dqblk)
	return -ENOSYS;
	return sb->s_qcop->set_dqblk(sb, type, id, &fdq);
	}

	static int quota_getxquota(struct super_block *sb, int type, qid_t id,
	void __user *addr)
	{
	struct fs_disk_quota fdq;
	int ret;

	if (!sb->s_qcop->get_dqblk)
	return -ENOSYS;
	ret = sb->s_qcop->get_dqblk(sb, type, id, &fdq);
	if (!ret && copy_to_user(addr, &fdq, sizeof(fdq)))
	return -EFAULT;
	return ret;
	}

	/* Copy parameters and call proper function */
	static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
	void __user *addr)
	{
	int ret;

	if (type >= (XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS))
	return -EINVAL;
	if (!sb->s_qcop)
	return -ENOSYS;

	ret = check_quotactl_permission(sb, type, cmd, id);
	if (ret < 0)
	return ret;

	switch (cmd) {
	case Q_QUOTAON:
	return quota_quotaon(sb, type, cmd, id, addr);
	case Q_QUOTAOFF:
	if (!sb->s_qcop->quota_off)
	return -ENOSYS;
	return sb->s_qcop->quota_off(sb, type, 0);
	case Q_GETFMT:
	return quota_getfmt(sb, type, addr);
	case Q_GETINFO:
	return quota_getinfo(sb, type, addr);
	case Q_SETINFO:
	return quota_setinfo(sb, type, addr);
	case Q_GETQUOTA:
	return quota_getquota(sb, type, id, addr);
	case Q_SETQUOTA:
	return quota_setquota(sb, type, id, addr);
	case Q_SYNC:
	if (!sb->s_qcop->quota_sync)
	return -ENOSYS;
	return sb->s_qcop->quota_sync(sb, type, 1);
	case Q_XQUOTAON:
	case Q_XQUOTAOFF:
	case Q_XQUOTARM:
	return quota_setxstate(sb, cmd, addr);
	case Q_XGETQSTAT:
	return quota_getxstate(sb, addr);
	case Q_XSETQLIM:
	return quota_setxquota(sb, type, id, addr);
	case Q_XGETQUOTA:
	return quota_getxquota(sb, type, id, addr);
	case Q_XQUOTASYNC:
	/* caller already holds s_umount */
	if (sb->s_flags & MS_RDONLY)
	return -EROFS;
	writeback_inodes_sb(sb);
	return 0;
	default:
	return -EINVAL;
	}
	}

	/*
	* look up a superblock on which quota ops will be performed
	* - use the name of a block device to find the superblock thereon
	*/
	static struct super_block quotactl_block(const char __user special)
	{
	#ifdef CONFIG_BLOCK
	struct block_device *bdev;
	struct super_block *sb;
	char *tmp = getname(special);

	if (IS_ERR(tmp))
	return ERR_CAST(tmp);
	bdev = lookup_bdev(tmp);
	putname(tmp);
	if (IS_ERR(bdev))
	return ERR_CAST(bdev);
	sb = get_super(bdev);
	bdput(bdev);
	if (!sb)
	return ERR_PTR(-ENODEV);

	return sb;
	#else
	return ERR_PTR(-ENODEV);
	#endif
	}

	/*
	* This is the system call interface. This communicates with
	* the user-level programs. Currently this only supports diskquota
	* calls. Maybe we need to add the process quotas etc. in the future,
	* but we probably should use rlimits for that.
	*/
	SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
	qid_t, id, void __user *, addr)
	{
	uint cmds, type;
	struct super_block *sb = NULL;
	int ret;

	cmds = cmd >> SUBCMDSHIFT;
	type = cmd & SUBCMDMASK;

	/*
	* As a special case Q_SYNC can be called without a specific device.
	* It will iterate all superblocks that have quota enabled and call
	* the sync action on each of them.
	*/
	if (!special) {
	if (cmds == Q_SYNC)
	return quota_sync_all(type);
	return -ENODEV;
	}

	sb = quotactl_block(special);
	if (IS_ERR(sb))
	return PTR_ERR(sb);

	ret = do_quotactl(sb, type, cmds, id, addr);

	drop_super(sb);
	return ret;
	}