[PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[Giedrius Statkevičius]

Remove the dead code protected by in_user in dgnc_tty_write() because it is set
to 0 and never changed to 1 thus the code in ifs never gets executed.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@gmail.com>
---
v2: Just remove the dead code protected by in_user and join the first and third
patches.

 drivers/staging/dgnc/dgnc_tty.c | 45 +----------------------------------------
 1 file changed, 1 insertion(+), 44 deletions(-)

diff --git a/drivers/staging/dgnc/dgnc_tty.c b/drivers/staging/dgnc/dgnc_tty.c
index ce4187f..cf2eb21 100644
--- a/drivers/staging/dgnc/dgnc_tty.c
+++ b/drivers/staging/dgnc/dgnc_tty.c
@@ -42,16 +42,11 @@
 #include "dgnc_sysfs.h"
 #include "dgnc_utils.h"
 
-#define init_MUTEX(sem)	 sema_init(sem, 1)
-#define DECLARE_MUTEX(name)     \
-	struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
-
 /*
  * internal variables
  */
 static struct dgnc_board	*dgnc_BoardsByMajor[256];
 static unsigned char		*dgnc_TmpWriteBuf;
-static DECLARE_MUTEX(dgnc_TmpWriteSem);
 
 /*
  * Default transparent print information.
@@ -1705,7 +1700,6 @@ static int dgnc_tty_write(struct tty_struct *tty,
 	ushort tail;
 	ushort tmask;
 	uint remain;
-	int from_user = 0;
 
 	if (tty == NULL || dgnc_TmpWriteBuf == NULL)
 		return 0;
@@ -1785,38 +1779,6 @@ static int dgnc_tty_write(struct tty_struct *tty,
 	if (count <= 0)
 		goto exit_retry;
 
-	if (from_user) {
-
-		count = min(count, WRITEBUFLEN);
-
-		spin_unlock_irqrestore(&ch->ch_lock, flags);
-
-		/*
-		 * If data is coming from user space, copy it into a temporary
-		 * buffer so we don't get swapped out while doing the copy to
-		 * the board.
-		 */
-		/* we're allowed to block if it's from_user */
-		if (down_interruptible(&dgnc_TmpWriteSem))
-			return -EINTR;
-
-		/*
-		 * copy_from_user() returns the number
-		 * of bytes that could *NOT* be copied.
-		 */
-		count -= copy_from_user(dgnc_TmpWriteBuf, (const unsigned char __user *) buf, count);
-
-		if (!count) {
-			up(&dgnc_TmpWriteSem);
-			return -EFAULT;
-		}
-
-		spin_lock_irqsave(&ch->ch_lock, flags);
-
-		buf = dgnc_TmpWriteBuf;
-
-	}
-
 	n = count;
 
 	/*
@@ -1853,12 +1815,7 @@ static int dgnc_tty_write(struct tty_struct *tty,
 		ch->ch_cpstime += (HZ * count) / ch->ch_digi.digi_maxcps;
 	}
 
-	if (from_user) {
-		spin_unlock_irqrestore(&ch->ch_lock, flags);
-		up(&dgnc_TmpWriteSem);
-	} else {
-		spin_unlock_irqrestore(&ch->ch_lock, flags);
-	}
+	spin_unlock_irqrestore(&ch->ch_lock, flags);
 
 	if (count) {
 		/*
-- 
2.3.5

[PATCH v2 2/2 RESEND] staging: dgnc: remove redundant check

[Giedrius Statkevičius]

count doesn't get changed in between identical checks in dgnc_tty_write() so
remove the second check

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@gmail.com>
---
v2: no change

 drivers/staging/dgnc/dgnc_tty.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/staging/dgnc/dgnc_tty.c b/drivers/staging/dgnc/dgnc_tty.c
index cf2eb21..61d5a8e 100644
--- a/drivers/staging/dgnc/dgnc_tty.c
+++ b/drivers/staging/dgnc/dgnc_tty.c
@@ -1773,12 +1773,6 @@ static int dgnc_tty_write(struct tty_struct *tty,
 		ch->ch_flags &= ~CH_PRON;
 	}
 
-	/*
-	 * If there is nothing left to copy, or I can't handle any more data, leave.
-	 */
-	if (count <= 0)
-		goto exit_retry;
-
 	n = count;
 
 	/*
-- 
2.3.5

Re: [PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[Sudip Mukherjee]

On Fri, Apr 10, 2015 at 05:48:54PM +0300, Giedrius Statkevičius wrote:
> Remove the dead code protected by in_user in dgnc_tty_write() because it is set
> to 0 and never changed to 1 thus the code in ifs never gets executed.
dgnc_tty_write() is being called by dgnc_tty_put_char() and it is also
the write callback function of struct tty_operations, so I think the
correct fix will be to use from_user and make it 0 when
dgnc_tty_put_char() calls this function else make it 1 to inform the
function that the data wil be coming from the userspace. Maybe some
thing like this:

diff --git a/drivers/staging/dgnc/dgnc_tty.c b/drivers/staging/dgnc/dgnc_tty.c
index ce4187f..96eaf5b 100644
--- a/drivers/staging/dgnc/dgnc_tty.c
+++ b/drivers/staging/dgnc/dgnc_tty.c
@@ -1682,10 +1682,15 @@ static int dgnc_tty_put_char(struct tty_struct *tty, unsigned char c)
 	/*
 	 * Simply call tty_write.
 	 */
-	dgnc_tty_write(tty, &c, 1);
+	__dgnc_tty_write(tty, &c, 1, 0);
 	return 1;
 }
 
+static int dgnc_tty_write(struct tty_struct *tty,
+		const unsigned char *buf, int count)
+{
+	__dgnc_tty_write(tty, buf, count, 1);
+}
 
 /*
  * dgnc_tty_write()
@@ -1693,8 +1698,8 @@ static int dgnc_tty_put_char(struct tty_struct *tty, unsigned char c)
  * Take data from the user or kernel and send it out to the FEP.
  * In here exists all the Transparent Print magic as well.
  */
-static int dgnc_tty_write(struct tty_struct *tty,
-		const unsigned char *buf, int count)
+static int __dgnc_tty_write(struct tty_struct *tty,
+		const unsigned char *buf, int count, int from_user)
 {
 	struct channel_t *ch = NULL;
 	struct un_t *un = NULL;
@@ -1705,7 +1710,6 @@ static int dgnc_tty_write(struct tty_struct *tty,
 	ushort tail;
 	ushort tmask;
 	uint remain;
-	int from_user = 0;
 
 	if (tty == NULL || dgnc_TmpWriteBuf == NULL)
 		return 0;


regards
sudip

Re: [PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[Giedrius Statkevičius]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1383 bytes --]

On Sat, 11 Apr 2015, Sudip Mukherjee wrote:

> On Fri, Apr 10, 2015 at 05:48:54PM +0300, Giedrius Statkevičius wrote:
> > Remove the dead code protected by in_user in dgnc_tty_write() because it is set
> > to 0 and never changed to 1 thus the code in ifs never gets executed.
> dgnc_tty_write() is being called by dgnc_tty_put_char() and it is also
> the write callback function of struct tty_operations, so I think the
> correct fix will be to use from_user and make it 0 when
> dgnc_tty_put_char() calls this function else make it 1 to inform the
> function that the data wil be coming from the userspace. Maybe some
> thing like this:
Well, I think this is wrong because:
* parameter of write member of struct tty_operations buf is not tagged with
  "__user" so it should be safe to just memcpy() from it
* Looked through some other write operations in other tty drivers and I've never
  seen copy_from_user() used on buf argument of write operation - always
  memcpy() or some other similar function
* Ldd3 (and the comments in tty_driver.h) says that write could be called from
  interrupt context too so it can't sleep and thus use copy_from_user()

While looking through I've caught that dgnc_TmpWriteBuf could be also deleted
because it will be unused if this patch goes through. If it does then I'll send
another one (or should I send a v3?)

Su pagarba / Regards,
Giedrius

Re: [PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[Sudip Mukherjee]

On Sat, Apr 11, 2015 at 03:20:43PM +0300, Giedrius Statkevičius wrote:
> On Sat, 11 Apr 2015, Sudip Mukherjee wrote:
> 
> > On Fri, Apr 10, 2015 at 05:48:54PM +0300, Giedrius Statkevičius wrote:
> Well, I think this is wrong because:

yes. I looked at many of the tty drivers and all of them have used
memcpy(). Sorry for my last mail, i should have written that after
seeing all other similar drivers and maybe once in a while i should
go back to LDD3. :)

regards
sudip

> 
> Su pagarba / Regards,
> Giedrius

Re: [PATCH v2 1/2 RESEND] staging: dgnc: remove dead code in dgnc_tty_write()

[Greg KH]

On Fri, Apr 10, 2015 at 05:48:54PM +0300, Giedrius Statkevičius wrote:
> Remove the dead code protected by in_user in dgnc_tty_write() because it is set
> to 0 and never changed to 1 thus the code in ifs never gets executed.

Please wrap your commit lines at 72 columns in the future.