Doug,
would this patch address the Linux kernel backward-compatibility concern you raised ?
Note, you would have to substitute the 3000 version by the appropriate version that introduced support for prin commands submitted on a open-ro device ...
--- sg_persist.c.orig 2014-05-04 01:10:01.987981956 +0200
+++ sg_persist.c 2014-05-04 20:44:34.665292548 +0200
@@ -16,6 +16,7 @@
#include <string.h>
#include <ctype.h>
#include <getopt.h>
+#include <sys/ioctl.h>
#define __STDC_FORMAT_MACROS 1
#include <inttypes.h>
@@ -26,6 +27,7 @@
#include "sg_lib.h"
#include "sg_cmds_basic.h"
#include "sg_cmds_extra.h"
+#include "sg_io_linux.h"
static const char * version_str = "0.44 20140202";
@@ -1029,6 +1031,8 @@
struct sg_simple_inquiry_resp inq_resp;
const char * cp;
struct opts_t opts;
+ int omode = 0;
+ const char *omode_desc = "rw";
memset(&opts, 0, sizeof(opts));
opts.prin = 1;
@@ -1292,10 +1296,31 @@
sg_cmds_close_device(sg_fd);
}
- if ((sg_fd = sg_cmds_open_device(device_name, 0 /* rw */,
+#ifdef SG_LIB_LINUX
+ /*
+ * PRIN commands do not provoke device changes, so we should avoid to
+ * open the device read-write so that the Linux kernel does not generate
+ * a change event.
+ * Older kernel do not support PRIN commands submission on a read-only
+ * opened device, so don't try in this case.
+ */
+ int v;
+ if (opts.prin) {
+ sg_fd = sg_cmds_open_device(device_name, 1, opts.verbose);
+ if (sg_fd >= 0) {
+ if (ioctl(sg_fd, SG_GET_VERSION_NUM, &v) >= 0 && v >= 30000) {
+ omode = 1;
+ omode_desc = "ro";
+ }
+ sg_cmds_close_device(sg_fd);
+ }
+ }
+#endif
+
+ if ((sg_fd = sg_cmds_open_device(device_name, omode,
opts.verbose)) < 0) {
- pr2serr("sg_persist: error opening file (rw): %s: %s\n", device_name,
- safe_strerror(-sg_fd));
+ pr2serr("sg_persist: error opening file (%s): %s: %s\n", omode_desc,
+ device_name, safe_strerror(-sg_fd));
return SG_LIB_FILE_ERROR;
}
Best regards,
Christophe Varoqui
On Sun, May 4, 2014 at 8:01 PM, Christophe Varoqui <christophe.varoqui@xxxxxxxxxxx> wrote:
Indeed, I'd rather let udev do its work on legitimate device changes. Problem is, this change event caused by sg_persist prin commands in not legitimate : no device change can be caused by interrogating the disk pr status.Doug informed me newer kernels accept prin commands inside a open-ro=>close sequence, which I now verified by testing with the patch I sent ... but older kernels do not. My patch is thus not backward compatible as-is.Any advice on how to treat this backward-compatibility issue ?For information, here's a more recent version of the patch I sent to Doug earlier to address not-Linux platform behaviour stability :--- sg_persist.c.orig 2014-05-04 01:10:01.987981956 +0200+++ sg_persist.c 2014-05-04 08:41:29.482017943 +0200@@ -1029,6 +1029,8 @@struct sg_simple_inquiry_resp inq_resp;const char * cp;struct opts_t opts;+ int omode = 0;+ const char *omode_desc = "rw";memset(&opts, 0, sizeof(opts));opts.prin = 1;@@ -1292,10 +1294,17 @@sg_cmds_close_device(sg_fd);}- if ((sg_fd = sg_cmds_open_device(device_name, 0 /* rw */,+#ifdef SG_LIB_LINUX+ if (opts.prin) {+ omode = 1;+ omode_desc = "ro";+ }+#endif++ if ((sg_fd = sg_cmds_open_device(device_name, omode,opts.verbose)) < 0) {- pr2serr("sg_persist: error opening file (rw): %s: %s\n", device_name,- safe_strerror(-sg_fd));+ pr2serr("sg_persist: error opening file (%s): %s: %s\n", omode_desc,+ device_name, safe_strerror(-sg_fd));return SG_LIB_FILE_ERROR;}Regards,Christophe VaroquiOn Sun, May 4, 2014 at 7:23 PM, Zdenek Kabelac <zkabelac@xxxxxxxxxx> wrote:Dne 4.5.2014 18:54, Hannes Reinecke napsal(a):When watch rule is disabled/removed in udev rules - your udev db becomes invalid when i.e. you run command like 'mkfs' - since the udev db will not be updated to list information about newly formatted filesystem.
On 05/04/2014 01:34 AM, Christophe Varoqui wrote:
It seems sg_persist is doing an "open rw => close" for --in commands,Yep.
causing a kernel change-event.
Look for 'watch' in the udev rules, that's precisely what it's doing.
(Bloody annoying if you ask me. Generally I recommend to remove that thing
from the rules).
Of course there are many cases where disabling watch rule makes sense
(i.e. you export lots of disks to virtual guests) - but unless you are
familiar with udev and you know what you are doing - think twice before disabling.
Zdenek
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