[PATCH v2 1/8] open device with O_NONBLOCK option

[David Disseldorp]

From: Alexey Svistunov <svalx@svalx.net>

When running the 2.6 kernel, "mt -f /dev/nst0 status" blocks if there is
no media in the drive.  The same occurs for other commands.

When running the 2.4.24 kernel, "mt -f /dev/nst0 status" does not block
when there is no tape in the drive.

This behavior change is documented for the 2.6 kernel (see
kernel-source-2.6.3/Documentation/scsi/st.txt for the full doc):

If the open option O_NONBLOCK is used, open succeeds even if the
drive is not ready. If O_NONBLOCK is not used, the driver waits for
the drive to become ready. If this does not happen in ST_BLOCK_SECONDS
seconds, open fails with the errno value EIO. With O_NONBLOCK the
device can be opened for writing even if there is a write protected
tape in the drive (commands trying to write something return error if
attempted).

It appears that the use of O_NONBLOCK is safe with pre-2.6 kernels.
Suggest adding the use of O_NONBLOCK when opening the device.  As it is,
for long-running commands such as "fsf", one cannot tell if the command is
progressing or if it's blocking waiting for media.

References: https://savannah.gnu.org/patch/?9263 & bsc#94449
---
 src/mt.c   | 4 ++--
 src/util.c | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/mt.c b/src/mt.c
index 8022b7c..ad81873 100644
--- a/src/mt.c
+++ b/src/mt.c
@@ -333,11 +333,11 @@ main (int argc, char **argv)
 #ifdef MTERASE
     case MTERASE:
 #endif
-      tapedesc = rmtopen (tapedev, O_WRONLY, 0, rsh_command_option);
+      tapedesc = rmtopen (tapedev, O_WRONLY | O_NONBLOCK, 0, 
rsh_command_option);
       break;
 
     default:
-      tapedesc = rmtopen (tapedev, O_RDONLY, 0, rsh_command_option);
+      tapedesc = rmtopen (tapedev, O_RDONLY | O_NONBLOCK, 0, 
rsh_command_option);
     }
   
   if (tapedesc == -1)
diff --git a/src/util.c b/src/util.c
index 996d4fa..346ced7 100644
--- a/src/util.c
+++ b/src/util.c
@@ -801,14 +801,14 @@ open_archive (char *file)
   copy_in = process_copy_in;
 
   if (copy_function == copy_in)
-    fd = rmtopen (file, O_RDONLY | O_BINARY, MODE_RW, rsh_command_option);
+    fd = rmtopen (file, O_RDONLY | O_BINARY | O_NONBLOCK, MODE_RW, 
rsh_command_option);
   else
     {
       if (!append_flag)
-       fd = rmtopen (file, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, MODE_RW,
+       fd = rmtopen (file, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | 
O_NONBLOCK, MODE_RW,
                        rsh_command_option);
       else
-       fd = rmtopen (file, O_RDWR | O_BINARY, MODE_RW, rsh_command_option);
+       fd = rmtopen (file, O_RDWR | O_BINARY | O_NONBLOCK, MODE_RW, 
rsh_command_option);
     }
 
   return fd;
-- 
2.26.2