[PATCH 11/11] compat_ioctl: move tape handling into drivers

[PATCH 11/11] compat_ioctl: move tape handling into drivers

[Arnd Bergmann]

MTIOCPOS and MTIOCGET are incompatible between 32-bit and 64-bit user
space, and traditionally have been translated in fs/compat_ioctl.c.

To get rid of that translation handler, move a corresponding
implementation into each of the four drivers implementing those commands.

The interesting part of that is now in a new linux/mtio.h header that
wraps the existing uapi/linux/mtio.h header and provides an abstraction
to let drivers handle both cases easily.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/ide/ide-tape.c        | 31 ++++++++++++----
 drivers/s390/char/tape_char.c | 41 ++++++++------------
 drivers/scsi/osst.c           | 34 ++++++++++-------
 drivers/scsi/st.c             | 35 +++++++++++-------
 fs/compat_ioctl.c             | 70 -----------------------------------
 include/linux/mtio.h          | 58 +++++++++++++++++++++++++++++
 6 files changed, 137 insertions(+), 132 deletions(-)
 create mode 100644 include/linux/mtio.h

diff --git a/drivers/ide/ide-tape.c b/drivers/ide/ide-tape.c
index 34c1165226a4..137febf3658d 100644
--- a/drivers/ide/ide-tape.c
+++ b/drivers/ide/ide-tape.c
@@ -19,6 +19,7 @@
 
 #define IDETAPE_VERSION "1.20"
 
+#include <linux/compat.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/string.h>
@@ -1368,7 +1369,7 @@ static int idetape_mtioctop(ide_drive_t *drive, short mt_op, int mt_count)
  * ide-tape ioctls are supported on both interfaces.
  */
 static long do_idetape_chrdev_ioctl(struct file *file,
-				unsigned int cmd, unsigned long arg)
+				unsigned int cmd, unsigned long arg, bool compat)
 {
 	struct ide_tape_obj *tape = file->private_data;
 	ide_drive_t *drive = tape->drive;
@@ -1407,14 +1408,10 @@ static long do_idetape_chrdev_ioctl(struct file *file,
 		if (tape->drv_write_prot)
 			mtget.mt_gstat |= GMT_WR_PROT(0xffffffff);
 
-		if (copy_to_user(argp, &mtget, sizeof(struct mtget)))
-			return -EFAULT;
-		return 0;
+		return put_user_mtget(argp, &mtget, compat);
 	case MTIOCPOS:
 		mtpos.mt_blkno = position / tape->user_bs_factor - block_offset;
-		if (copy_to_user(argp, &mtpos, sizeof(struct mtpos)))
-			return -EFAULT;
-		return 0;
+		return put_user_mtpos(argp, &mtpos, compat);
 	default:
 		if (tape->chrdev_dir == IDETAPE_DIR_READ)
 			ide_tape_discard_merge_buffer(drive, 1);
@@ -1427,7 +1424,23 @@ static long idetape_chrdev_ioctl(struct file *file,
 {
 	long ret;
 	mutex_lock(&ide_tape_mutex);
-	ret = do_idetape_chrdev_ioctl(file, cmd, arg);
+	ret = do_idetape_chrdev_ioctl(file, cmd, arg, false);
+	mutex_unlock(&ide_tape_mutex);
+	return ret;
+}
+
+static long idetape_chrdev_compat_ioctl(struct file *file,
+				unsigned int cmd, unsigned long arg)
+{
+	long ret;
+
+	if (cmd == MTIOCPOS32)
+		cmd = MTIOCPOS;
+	else if (cmd == MTIOCGET32)
+		cmd = MTIOCGET;
+
+	mutex_lock(&ide_tape_mutex);
+	ret = do_idetape_chrdev_ioctl(file, cmd, arg, true);
 	mutex_unlock(&ide_tape_mutex);
 	return ret;
 }
@@ -1886,6 +1899,8 @@ static const struct file_operations idetape_fops = {
 	.read		= idetape_chrdev_read,
 	.write		= idetape_chrdev_write,
 	.unlocked_ioctl	= idetape_chrdev_ioctl,
+	.compat_ioctl	= IS_ENABLED(CONFIG_COMPAT) ?
+			  idetape_chrdev_compat_ioctl : NULL,
 	.open		= idetape_chrdev_open,
 	.release	= idetape_chrdev_release,
 	.llseek		= noop_llseek,
diff --git a/drivers/s390/char/tape_char.c b/drivers/s390/char/tape_char.c
index fc206c9d1c56..522ca9b836e3 100644
--- a/drivers/s390/char/tape_char.c
+++ b/drivers/s390/char/tape_char.c
@@ -341,14 +341,14 @@ tapechar_release(struct inode *inode, struct file *filp)
  */
 static int
 __tapechar_ioctl(struct tape_device *device,
-		 unsigned int no, unsigned long data)
+		 unsigned int no, void __user *data, bool compat)
 {
 	int rc;
 
 	if (no == MTIOCTOP) {
 		struct mtop op;
 
-		if (copy_from_user(&op, (char __user *) data, sizeof(op)) != 0)
+		if (copy_from_user(&op, data, sizeof(op)) != 0)
 			return -EFAULT;
 		if (op.mt_count < 0)
 			return -EINVAL;
@@ -392,9 +392,7 @@ __tapechar_ioctl(struct tape_device *device,
 		if (rc < 0)
 			return rc;
 		pos.mt_blkno = rc;
-		if (copy_to_user((char __user *) data, &pos, sizeof(pos)) != 0)
-			return -EFAULT;
-		return 0;
+		return put_user_mtpos(data, &pos, compat);
 	}
 	if (no == MTIOCGET) {
 		/* MTIOCGET: query the tape drive status. */
@@ -424,15 +422,12 @@ __tapechar_ioctl(struct tape_device *device,
 			get.mt_blkno = rc;
 		}
 
-		if (copy_to_user((char __user *) data, &get, sizeof(get)) != 0)
-			return -EFAULT;
-
-		return 0;
+		return put_user_mtget(data, &get, compat);
 	}
 	/* Try the discipline ioctl function. */
 	if (device->discipline->ioctl_fn == NULL)
 		return -EINVAL;
-	return device->discipline->ioctl_fn(device, no, data);
+	return device->discipline->ioctl_fn(device, no, (unsigned long)data);
 }
 
 static long
@@ -445,7 +440,7 @@ tapechar_ioctl(struct file *filp, unsigned int no, unsigned long data)
 
 	device = (struct tape_device *) filp->private_data;
 	mutex_lock(&device->mutex);
-	rc = __tapechar_ioctl(device, no, data);
+	rc = __tapechar_ioctl(device, no, (void __user *)data, false);
 	mutex_unlock(&device->mutex);
 	return rc;
 }
@@ -455,23 +450,17 @@ static long
 tapechar_compat_ioctl(struct file *filp, unsigned int no, unsigned long data)
 {
 	struct tape_device *device = filp->private_data;
-	int rval = -ENOIOCTLCMD;
-	unsigned long argp;
+	long rc;
 
-	/* The 'arg' argument of any ioctl function may only be used for
-	 * pointers because of the compat pointer conversion.
-	 * Consider this when adding new ioctls.
-	 */
-	argp = (unsigned long) compat_ptr(data);
-	if (device->discipline->ioctl_fn) {
-		mutex_lock(&device->mutex);
-		rval = device->discipline->ioctl_fn(device, no, argp);
-		mutex_unlock(&device->mutex);
-		if (rval == -EINVAL)
-			rval = -ENOIOCTLCMD;
-	}
+	if (no == MTIOCPOS32)
+		no = MTIOCPOS;
+	else if (no == MTIOCGET32)
+		no = MTIOCGET;
 
-	return rval;
+	mutex_lock(&device->mutex);
+	rc = __tapechar_ioctl(device, no, compat_ptr(data), false);
+	mutex_unlock(&device->mutex);
+	return rc;
 }
 #endif /* CONFIG_COMPAT */
 
diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
index 7a1a1edde35d..842457b9134a 100644
--- a/drivers/scsi/osst.c
+++ b/drivers/scsi/osst.c
@@ -33,6 +33,7 @@ static const char * osst_version = "0.99.4";
 
 #include <linux/module.h>
 
+#include <linux/compat.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
 #include <linux/sched/signal.h>
@@ -4941,7 +4942,7 @@ static int os_scsi_tape_close(struct inode * inode, struct file * filp)
 static long osst_ioctl(struct file * file,
 	 unsigned int cmd_in, unsigned long arg)
 {
-	int		      i, cmd_nr, cmd_type, blk, retval = 0;
+	int		      i, cmd_nr, cmd_type, cmd_size, blk, retval = 0;
 	struct st_modedef   * STm;
 	struct st_partstat  * STps;
 	struct osst_request * SRpnt = NULL;
@@ -4978,6 +4979,7 @@ static long osst_ioctl(struct file * file,
 
 	cmd_type = _IOC_TYPE(cmd_in);
 	cmd_nr   = _IOC_NR(cmd_in);
+	cmd_size = _IOC_SIZE(cmd_in);
 #if DEBUG
 	printk(OSST_DEB_MSG "%s:D: Ioctl %d,%d in %s mode\n", name,
 			    cmd_type, cmd_nr, STp->raw?"raw":"normal");
@@ -5179,7 +5181,8 @@ static long osst_ioctl(struct file * file,
 	if (cmd_type == _IOC_TYPE(MTIOCGET) && cmd_nr == _IOC_NR(MTIOCGET)) {
 		struct mtget mt_status;
 
-		if (_IOC_SIZE(cmd_in) != sizeof(struct mtget)) {
+		if (cmd_size != sizeof(struct mtget) &&
+		    cmd_size != sizeof(struct mtget32)) {
 			 retval = (-EINVAL);
 			 goto out;
 		}
@@ -5229,21 +5232,18 @@ static long osst_ioctl(struct file * file,
 		    STp->drv_buffer != 0)
 			mt_status.mt_gstat |= GMT_IM_REP_EN(0xffffffff);
 
-		i = copy_to_user(p, &mt_status, sizeof(struct mtget));
-		if (i) {
-			retval = (-EFAULT);
-			goto out;
-		}
-
-		STp->recover_erreg = 0;  /* Clear after read */
-		retval = 0;
+		retval = put_user_mtget(p, &mt_status,
+					cmd_size == sizeof(struct mtget32));
+		if (!retval)
+			STp->recover_erreg = 0;  /* Clear after read */
 		goto out;
 	} /* End of MTIOCGET */
 
 	if (cmd_type == _IOC_TYPE(MTIOCPOS) && cmd_nr == _IOC_NR(MTIOCPOS)) {
 		struct mtpos mt_pos;
 
-		if (_IOC_SIZE(cmd_in) != sizeof(struct mtpos)) {
+		if (cmd_size != sizeof(struct mtpos) &&
+		    cmd_size != sizeof(struct mtpos32)) {
 			retval = (-EINVAL);
 			goto out;
 		}
@@ -5256,9 +5256,7 @@ static long osst_ioctl(struct file * file,
 			goto out;
 		}
 		mt_pos.mt_blkno = blk;
-		i = copy_to_user(p, &mt_pos, sizeof(struct mtpos));
-		if (i)
-			retval = -EFAULT;
+		retval = put_user_mtpos(p, &mt_pos, cmd_size == sizeof(struct mtpos32));
 		goto out;
 	}
 	if (SRpnt) osst_release_request(SRpnt);
@@ -5284,6 +5282,14 @@ static long osst_compat_ioctl(struct file * file, unsigned int cmd_in, unsigned
 	struct osst_tape *STp = file->private_data;
 	struct scsi_device *sdev = STp->device;
 	int ret = -ENOIOCTLCMD;
+
+	switch (cmd_in) {
+	case MTIOCTOP:
+	case MTIOCPOS32:
+	case MTIOCGET32:
+		return osst_ioctl(file, cmd_in, (unsigned long)compat_ptr(arg));
+	}
+
 	if (sdev->host->hostt->compat_ioctl) {
 
 		ret = sdev->host->hostt->compat_ioctl(sdev, cmd_in, (void __user *)arg);
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 307df2fa39a3..62244ce53baa 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -21,6 +21,7 @@ static const char *verstr = "20160209";
 
 #include <linux/module.h>
 
+#include <linux/compat.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
 #include <linux/sched/signal.h>
@@ -3498,7 +3499,7 @@ static int partition_tape(struct scsi_tape *STp, int size)
 /* The ioctl command */
 static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 {
-	int i, cmd_nr, cmd_type, bt;
+	int i, cmd_nr, cmd_type, cmd_size, bt;
 	int retval = 0;
 	unsigned int blk;
 	struct scsi_tape *STp = file->private_data;
@@ -3532,6 +3533,7 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 
 	cmd_type = _IOC_TYPE(cmd_in);
 	cmd_nr = _IOC_NR(cmd_in);
+	cmd_size = _IOC_SIZE(cmd_in);
 
 	if (cmd_type == _IOC_TYPE(MTIOCTOP) && cmd_nr == _IOC_NR(MTIOCTOP)) {
 		struct mtop mtc;
@@ -3741,7 +3743,8 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 	if (cmd_type == _IOC_TYPE(MTIOCGET) && cmd_nr == _IOC_NR(MTIOCGET)) {
 		struct mtget mt_status;
 
-		if (_IOC_SIZE(cmd_in) != sizeof(struct mtget)) {
+		if (cmd_size != sizeof(struct mtget) &&
+		    cmd_size != sizeof(struct mtget32)) {
 			 retval = (-EINVAL);
 			 goto out;
 		}
@@ -3796,19 +3799,16 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 		if (STp->cleaning_req)
 			mt_status.mt_gstat |= GMT_CLN(0xffffffff);
 
-		i = copy_to_user(p, &mt_status, sizeof(struct mtget));
-		if (i) {
-			retval = (-EFAULT);
-			goto out;
-		}
+		retval = put_user_mtget(p, &mt_status,
+					cmd_size == sizeof(struct mtget32));
 
 		STp->recover_reg = 0;		/* Clear after read */
-		retval = 0;
 		goto out;
 	}			/* End of MTIOCGET */
 	if (cmd_type == _IOC_TYPE(MTIOCPOS) && cmd_nr == _IOC_NR(MTIOCPOS)) {
 		struct mtpos mt_pos;
-		if (_IOC_SIZE(cmd_in) != sizeof(struct mtpos)) {
+		if (cmd_size != sizeof(struct mtpos) &&
+		    cmd_size != sizeof(struct mtpos32)) {
 			 retval = (-EINVAL);
 			 goto out;
 		}
@@ -3817,9 +3817,8 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 			goto out;
 		}
 		mt_pos.mt_blkno = blk;
-		i = copy_to_user(p, &mt_pos, sizeof(struct mtpos));
-		if (i)
-			retval = (-EFAULT);
+		retval = put_user_mtpos(p, &mt_pos,
+					cmd_size == sizeof(struct mtpos32));
 		goto out;
 	}
 	mutex_unlock(&STp->lock);
@@ -3853,14 +3852,22 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 }
 
 #ifdef CONFIG_COMPAT
-static long st_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+static long st_compat_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 {
 	struct scsi_tape *STp = file->private_data;
 	struct scsi_device *sdev = STp->device;
 	int ret = -ENOIOCTLCMD;
+
+	switch (cmd_in) {
+	case MTIOCTOP:
+	case MTIOCPOS32:
+	case MTIOCGET32:
+		return st_ioctl(file, cmd_in, (unsigned long)compat_ptr(arg));
+	}
+
 	if (sdev->host->hostt->compat_ioctl) { 
 
-		ret = sdev->host->hostt->compat_ioctl(sdev, cmd, (void __user *)arg);
+		ret = sdev->host->hostt->compat_ioctl(sdev, cmd_in, (void __user *)arg);
 
 	}
 	return ret;
diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index bb73d52f02a2..70db940aeea9 100644
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -35,7 +35,6 @@
 #include <linux/ppp_defs.h>
 #include <linux/ppp-ioctl.h>
 #include <linux/if_pppox.h>
-#include <linux/mtio.h>
 #include <linux/tty.h>
 #include <linux/vt_kern.h>
 #include <linux/fb.h>
@@ -265,70 +264,6 @@ static int sg_ioctl_trans(struct file *file, unsigned int cmd,
 	return err;
 }
 
-struct mtget32 {
-	compat_long_t	mt_type;
-	compat_long_t	mt_resid;
-	compat_long_t	mt_dsreg;
-	compat_long_t	mt_gstat;
-	compat_long_t	mt_erreg;
-	compat_daddr_t	mt_fileno;
-	compat_daddr_t	mt_blkno;
-};
-#define MTIOCGET32	_IOR('m', 2, struct mtget32)
-
-struct mtpos32 {
-	compat_long_t	mt_blkno;
-};
-#define MTIOCPOS32	_IOR('m', 3, struct mtpos32)
-
-static int mt_ioctl_trans(struct file *file,
-		unsigned int cmd, void __user *argp)
-{
-	/* NULL initialization to make gcc shut up */
-	struct mtget __user *get = NULL;
-	struct mtget32 __user *umget32;
-	struct mtpos __user *pos = NULL;
-	struct mtpos32 __user *upos32;
-	unsigned long kcmd;
-	void *karg;
-	int err = 0;
-
-	switch(cmd) {
-	case MTIOCPOS32:
-		kcmd = MTIOCPOS;
-		pos = compat_alloc_user_space(sizeof(*pos));
-		karg = pos;
-		break;
-	default:	/* MTIOCGET32 */
-		kcmd = MTIOCGET;
-		get = compat_alloc_user_space(sizeof(*get));
-		karg = get;
-		break;
-	}
-	if (karg == NULL)
-		return -EFAULT;
-	err = do_ioctl(file, kcmd, (unsigned long)karg);
-	if (err)
-		return err;
-	switch (cmd) {
-	case MTIOCPOS32:
-		upos32 = argp;
-		err = convert_in_user(&pos->mt_blkno, &upos32->mt_blkno);
-		break;
-	case MTIOCGET32:
-		umget32 = argp;
-		err = convert_in_user(&get->mt_type, &umget32->mt_type);
-		err |= convert_in_user(&get->mt_resid, &umget32->mt_resid);
-		err |= convert_in_user(&get->mt_dsreg, &umget32->mt_dsreg);
-		err |= convert_in_user(&get->mt_gstat, &umget32->mt_gstat);
-		err |= convert_in_user(&get->mt_erreg, &umget32->mt_erreg);
-		err |= convert_in_user(&get->mt_fileno, &umget32->mt_fileno);
-		err |= convert_in_user(&get->mt_blkno, &umget32->mt_blkno);
-		break;
-	}
-	return err ? -EFAULT: 0;
-}
-
 #endif /* CONFIG_BLOCK */
 
 /* Bluetooth ioctls */
@@ -544,8 +479,6 @@ COMPATIBLE_IOCTL(SCSI_IOCTL_GET_PCI)
  */
 COMPATIBLE_IOCTL(_IOR('p', 20, int[7])) /* RTCGET */
 COMPATIBLE_IOCTL(_IOW('p', 21, int[7])) /* RTCSET */
-/* Little m */
-COMPATIBLE_IOCTL(MTIOCTOP)
 /* Socket level stuff */
 COMPATIBLE_IOCTL(FIOQSIZE)
 #ifdef CONFIG_BLOCK
@@ -657,9 +590,6 @@ static long do_ioctl_trans(unsigned int cmd,
 #ifdef CONFIG_BLOCK
 	case SG_IO:
 		return sg_ioctl_trans(file, cmd, argp);
-	case MTIOCGET32:
-	case MTIOCPOS32:
-		return mt_ioctl_trans(file, cmd, argp);
 #endif
 	/* Serial */
 	case TIOCGSERIAL:
diff --git a/include/linux/mtio.h b/include/linux/mtio.h
new file mode 100644
index 000000000000..02640756a40d
--- /dev/null
+++ b/include/linux/mtio.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MTIO_COMPAT_H
+#define _LINUX_MTIO_COMPAT_H
+
+#include <uapi/linux/mtio.h>
+#include <linux/uaccess.h>
+
+/*
+ * helper functions for implementing compat ioctls on the four tape
+ * drivers: we define the 32-bit layout of each incompatible strucucture,
+ * plus a wrapper function to copy it to user space in either format.
+ */
+
+struct	mtget32 {
+	s32	mt_type;
+	s32	mt_resid;
+	s32	mt_dsreg;
+	s32	mt_gstat;
+	s32	mt_erreg;
+	s32	mt_fileno;
+	s32	mt_blkno;
+};
+#define	MTIOCGET32	_IOR('m', 2, struct mtget32)
+
+struct	mtpos32 {
+	s32 	mt_blkno;
+};
+#define	MTIOCPOS32	_IOR('m', 3, struct mtpos32)
+
+static inline int put_user_mtget(void __user *u, struct mtget *k, bool compat)
+{
+	struct mtget32 k32 = {
+		.mt_type   = k->mt_type,
+		.mt_resid  = k->mt_resid,
+		.mt_dsreg  = k->mt_dsreg,
+		.mt_gstat  = k->mt_gstat,
+		.mt_fileno = k->mt_fileno,
+		.mt_blkno  = k->mt_blkno,
+	};
+	int ret;
+
+	if (IS_ENABLED(CONFIG_COMPAT) && compat)
+		ret = copy_to_user(u, &k32, sizeof(k32));
+	else
+		ret = copy_to_user(u, k, sizeof(*k));
+
+	return ret ? -EFAULT : 0;
+}
+
+static inline int put_user_mtpos(void __user *u, struct mtpos *k, bool compat)
+{
+	if (IS_ENABLED(CONFIG_COMPAT) && compat)
+		return put_user(k->mt_blkno, (u32 __user *)u);
+	else
+		return put_user(k->mt_blkno, (long __user *)u);
+}
+
+#endif
-- 
2.18.0

Re: [PATCH 11/11] compat_ioctl: move tape handling into drivers

[Al Viro]

On Sat, Sep 08, 2018 at 04:28:17PM +0200, Arnd Bergmann wrote:
> MTIOCPOS and MTIOCGET are incompatible between 32-bit and 64-bit user
> space, and traditionally have been translated in fs/compat_ioctl.c.
> 
> To get rid of that translation handler, move a corresponding
> implementation into each of the four drivers implementing those commands.
> 
> The interesting part of that is now in a new linux/mtio.h header that
> wraps the existing uapi/linux/mtio.h header and provides an abstraction
> to let drivers handle both cases easily.

Ugh...  Frankly, this bool compat passed all way down looks wrong.
I can live with that; the question is whether block folks will be
OK with that thing...

Re: [PATCH 11/11] compat_ioctl: move tape handling into drivers

[Arnd Bergmann]

On Sun, Sep 9, 2018 at 6:38 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Sat, Sep 08, 2018 at 04:28:17PM +0200, Arnd Bergmann wrote:
> > MTIOCPOS and MTIOCGET are incompatible between 32-bit and 64-bit user
> > space, and traditionally have been translated in fs/compat_ioctl.c.
> >
> > To get rid of that translation handler, move a corresponding
> > implementation into each of the four drivers implementing those commands.
> >
> > The interesting part of that is now in a new linux/mtio.h header that
> > wraps the existing uapi/linux/mtio.h header and provides an abstraction
> > to let drivers handle both cases easily.
>
> Ugh...  Frankly, this bool compat passed all way down looks wrong.
> I can live with that; the question is whether block folks will be
> OK with that thing...

I have tried to come up with an alternative, but couldn't really find anything
that is less ugly. Since nobody else complained, I'll resend this version
along with the other patches.

       Arnd

Re: [PATCH 11/11] compat_ioctl: move tape handling into drivers

[Arnd Bergmann]

On Tue, Sep 11, 2018 at 5:36 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Sun, Sep 9, 2018 at 6:38 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Sat, Sep 08, 2018 at 04:28:17PM +0200, Arnd Bergmann wrote:
> > > MTIOCPOS and MTIOCGET are incompatible between 32-bit and 64-bit user
> > > space, and traditionally have been translated in fs/compat_ioctl.c.
> > >
> > > To get rid of that translation handler, move a corresponding
> > > implementation into each of the four drivers implementing those commands.
> > >
> > > The interesting part of that is now in a new linux/mtio.h header that
> > > wraps the existing uapi/linux/mtio.h header and provides an abstraction
> > > to let drivers handle both cases easily.
> >
> > Ugh...  Frankly, this bool compat passed all way down looks wrong.
> > I can live with that; the question is whether block folks will be
> > OK with that thing...
>
> I have tried to come up with an alternative, but couldn't really find anything
> that is less ugly. Since nobody else complained, I'll resend this version
> along with the other patches.

Actually, there was one idea that Deepa mentioned for another subsystem
with a similar issue: instead of passing down the fact that we come from
a compat syscall through multiple function calls, the lowest ones
(put_user_mtpos, put_user_mtget) could call in_compat_syscall().

Would you prefer that?

      Arnd