Utilize new IMPORT{db} udev rule to repopulate udev db for spurious events
PATCH 1/1 Utilize new IMPORT{db} udev rule to repopulate udev db for spurious events
Udev v152 was released just today. This one adds new IMPORT{db}="<property_name>" udev rule that reads a single value from udev database identified by property_name.
We can use this rule to (partially) support artificial events (e.g. the ones generated as a result of "udevadm trigger" call or the "watch" udev rule). These spurious events do not have the flags set which we use to direct the rule application. The old values could not be read from udev db because it was always cleared on ADD and CHANGE events making.
Now, we can use new IMPORT{db} rule to repopulate udev db content if such situation occurs. I've added new DM_UDEV_PRIMARY_SOURCE_FLAG so we can easily separate events and identify the ones which originate in libdevmapper. For all the other ones, we will try to reuse existing information that is currently in udev db.
However, we still can't synchronize with those spurious events, but at least it is a step forward and one problem less.
(Looking more at the udev changelog, "udevadm trigger" generates CHANGE events by default from now on, so this helps us a little too - people calling *plain* udevadm trigger won't lose their nodes/symlinks for DM devices anymore. People can still call "udevadm trigger --action=add" though and need to be aware of what the consequences of reacting to ADD events are for DM devices!)
Peter
--- libdm/ioctl/libdm-iface.c | 59 +++++++++++++++++++++++++++----------------- libdm/libdevmapper.h | 10 +++++++ tools/dmsetup.c | 3 +- udev/10-dm.rules.in | 22 ++++++++++++++++ 4 files changed, 70 insertions(+), 24 deletions(-)
libdm/ioctl/libdm-iface.c +36 -23
@@ -1736,31 +1736,44 @@ static struct dm_ioctl *_do_dm_ioctl(struct dm_task *dmt, unsigned command, dmt->type ==DM_DEVICE_REMOVE || dmt->type ==DM_DEVICE_RENAME ; -/* -* Prevent udev vs. libdevmapper race when processing nodes and -* symlinks. This can happen when the udev rules are installed and -* udev synchronisation code is enabled in libdevmapper but the -* software using libdevmapper does not make use of it (by not calling -* dm_task_set_cookie before). We need to instruct the udev rules not -* to be applied at all in this situation so we can gracefully fallback -* to libdevmapper's node and symlink creation code. -*/ -if (dm_udev_get_sync_support () && !dmt->cookie_set && ioctl_with_uevent) { -log_debug ("Cookie value is not set while trying to call " -"DM_DEVICE_RESUME, DM_DEVICE_REMOVE or DM_DEVICE_RENAME " -"ioctl. Please, consider using libdevmapper's udev " -"synchronisation interface or disable it explicitly " -"by calling dm_udev_set_sync_support(0)." ); -log_debug ("Switching off device-mapper and all subsystem related " -"udev rules. Falling back to libdevmapper node creation." ); +if (ioctl_with_uevent &&dm_cookie_supported ()) {/* -* Disable general dm and subsystem rules but keep dm disk rules -* if not flagged out explicitly before. We need /dev/disk content -* for the software that expects it. -*/ - dmi->event_nr |= (DM_UDEV_DISABLE_DM_RULES_FLAG | -DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG ) << +* Always mark events coming from libdevmapper as +* "primary sourced". This is needed to distinguish +* any spurious events so we can act appropriately. +* This needs to be applied even when udev_sync is +* not used because udev flags could be used alone. +*/ + dmi->event_nr |=DM_UDEV_PRIMARY_SOURCE_FLAG <<DM_UDEV_FLAGS_SHIFT ; + +/* +* Prevent udev vs. libdevmapper race when processing nodes +* and symlinks. This can happen when the udev rules are +* installed and udev synchronisation code is enabled in +* libdevmapper but the software using libdevmapper does not +* make use of it (by not calling dm_task_set_cookie before). +* We need to instruct the udev rules not to be applied at +* all in this situation so we can gracefully fallback to +* libdevmapper's node and symlink creation code. +*/ +if (!dmt->cookie_set &&dm_udev_get_sync_support ()) { +log_debug ("Cookie value is not set while trying to call " +"DM_DEVICE_RESUME, DM_DEVICE_REMOVE or DM_DEVICE_RENAME " +"ioctl. Please, consider using libdevmapper's udev " +"synchronisation interface or disable it explicitly " +"by calling dm_udev_set_sync_support(0)." ); +log_debug ("Switching off device-mapper and all subsystem related " +"udev rules. Falling back to libdevmapper node creation." ); +/* +* Disable general dm and subsystem rules but keep +* dm disk rules if not flagged out explicitly before. +* We need /dev/disk content for the software that expects it. +*/ + dmi->event_nr |= (DM_UDEV_DISABLE_DM_RULES_FLAG | +DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG ) << +DM_UDEV_FLAGS_SHIFT ; + } } log_debug("dm %s %s %s%s%s %s%.0d%s%.0d%s"
libdm/libdevmapper.h +10 -0
@@ -1092,6 +1092,16 @@ void dm_report_field_set_value(struct dm_report_field *field, const void *value,* udev does something improperly. */ #define DM_UDEV_DISABLE_LIBRARY_FALLBACK 0x0020 +/* +* DM_UDEV_PRIMARY_SOURCE_FLAG is automatically appended by +* libdevmapper for all ioctls generating udev uevents. Once used in +* udev rules, we know if this is a real "primary sourced" event or not. +* We need to distinguish real events originated in libdevmapper from +* any spurious events to gather all missing information (e.g. events +* generated as a result of "udevadm trigger" command or as a result +* of the "watch" udev rule). +*/ +#define DM_UDEV_PRIMARY_SOURCE_FLAG 0x0040int dm_cookie_supported (void );
tools/dmsetup.c +2 -1
@@ -842,7 +842,8 @@ static int _udevflags(int args, char **argv, void *data __attribute((unused)))"DISABLE_OTHER_RULES" ,"LOW_PRIORITY" ,"DISABLE_LIBRARY_FALLBACK" , - 0, 0}; +"PRIMARY_SOURCE" , + 0};if (!(cookie =_get_cookie_value (argv[1 ])))return 0 ;
udev/10-dm.rules.in +22 -0
@@ -44,6 +44,28 @@ ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env ACTION!="add|change", GOTO="dm_end" +# There is no cookie set nor any flags encoded in events not originating +# in libdevmapper so we need to detect this and try to behave correctly. +# For such spurious events, regenerate all flags from current udev databse content +# (this information would normally be inaccessible for ADD and CHANGE events). +ENV{DM_UDEV_PRIMARY_SOURCE_FLAG}=="1", GOTO="dm_flags_done" +IMPORT{db}="DM_UDEV_DISABLE_DM_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_DISK_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_OTHER_RULES_FLAG" +IMPORT{db}="DM_UDEV_LOW_PRIORITY_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_LIBRARY_FALLBACK_FLAG" +IMPORT{db}="DM_UDEV_FLAG7" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG0" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG1" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG2" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG3" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG4" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG5" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG6" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG7" +LABEL="dm_flags_done" + # Normally, we operate on "change" events only. But when # coldplugging, there's an "add" event present. We have to # recognize this and do our actions in this particular
PATCH 1/1 Utilize new IMPORT{db} udev rule to repopulate udev db for spurious events
Quoted 5 lines · Peter Rajnoha
udev/10-dm.rules.in +5
-0+IMPORT{db}="DM_UDEV_DISABLE_DM_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_DISK_RULES_FLAG" +IMPORT{db}="DM_UDEV_DISABLE_OTHER_RULES_FLAG" +IMPORT{db}="DM_UDEV_LOW_PRIORITY_FLAG"
udev/10-dm.rules.in ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env · line 66
Quoted 10 lines
udev/10-dm.rules.in +10
-0+IMPORT{db}="DM_UDEV_DISABLE_LIBRARY_FALLBACK_FLAG" +IMPORT{db}="DM_UDEV_FLAG7" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG0" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG1" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG2" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG3" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG4" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG5" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG6" +IMPORT{db}="DM_SUBSYSTEM_UDEV_FLAG7"
...just for the record - the IMPORT{db} rule does not support pattern matching (not now at least), so that's the reason why I have to write it this way instead of something like IMPORT{db}="DM_*_FLAG".
Peter
PATCH 1/1 Utilize new IMPORT{db} udev rule to repopulate udev db for spurious events
In reply to Peter Rajnohaudev/10-dm.rules.in ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env · line 45
Quoted 3 lines · Peter Rajnoha
udev/10-dm.rules.in +1
-0@@ -44,6 +44,28 @@ ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env +IMPORT{db}="DM_UDEV_DISABLE_DM_RULES_FLAG"
How does this cope if an older version of udev is installed?
Do we need to install/activate it conditionally?
Alasdair
PATCH 1/1 Utilize new IMPORT{db} udev rule to repopulate udev db for spurious events
Quoted 8 lines · Alasdair G Kergon
udev/10-dm.rules.in ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env · line 45
Quoted 3 lines · Peter Rajnoha
udev/10-dm.rules.in +1
-0@@ -44,6 +44,28 @@ ENV{DM_COOKIE}=="?*", IMPORT{program}="$env{DM_SBIN_PATH}/dmsetup udevflags $env +IMPORT{db}="DM_UDEV_DISABLE_DM_RULES_FLAG"How does this cope if an older version of udev is installed?
Do we need to install/activate it conditionally?
Good question! We'll probably need to do something like that. Looking precisely at udevd debug log:
- it tries to fallback to "auto mode" if it can't recognize the type of IMPORT
- it tries to stat the file with the name given as parameter, e.g. "DM_UDEV_DISABLE_DM_RULES_FLAG"
- if it's not a valid path, it will put "/lib/udev/" as a prefix first, so we'll have "/lib/udev/disable/DM_UDEV_DISBALE_DM_RULES_FLAG"
- if the file *really exists* by chance then:
- it will try to execute it if it has executable flag set (fallback to IMPORT{program})
- it will try to read the contents of it (fallback to IMPORT{file})
Hmm, this definitely needs to be taken care of...
Peter