This patchset started out as a simple patch to introduce the irqs command from Android's FIQ debugger to kdb. However it has since grown more powerful because allowing kdb to reuse existing kernel infrastructure gives us extra opportunities.
Based on the comments at the top of irqdesc.h (plotting to take the irq_desc structure private to kernel/irq) and the relative similarity between FIQ debugger's irqs command and the contents /proc/interrupts we start by adding a kdb feature to print seq_files. This forms the foundation for a new command, interrupts.
I have also been able to implement a much more generic command, seq_file, that can display a good number of files from pseudo filesystems. This command is very powerful although that power does mean care must be taken to deploy it safely. It is deliberately and by default aimed at your foot!
Note that the risk associated with the seq_file command is why I implemented the interrupts command in C (in principle it could have been a kdb macro). Doing it in C codifies the need for show_interrupts() to continue using spin locks as its locking strategy.
To give an idea of what can be done with this command. The following seq_operations structures worked correctly and report no errors:
cpuinfo_op extfrag_op fragmentation_op gpiolib_seq_ops int_seq_ops (a.k.a. /proc/interrupts) pagetypeinfo_op unusable_op vmalloc_op zoneinfo_op
The following display the information correctly but triggered errors (sleeping function called from invalid context) with lock debugging enabled:
consoles_op crypto_seq_ops diskstats_op partitions_op slabinfo_op vmstat_op
All tests are run on an ARM multi_v7_defconfig kernel (plus lots of debug features) and halted using magic SysRq so that kdb has interrupt context. Note also that some of the seq_operations structures hook into driver supplied code that will only be called if that driver is enabled so the test above are useful but cannot be exhaustive.
Changes since v1: * Added nop inline version of kdb_print_seq_file() and used it to fix build error when CONFIG_KGDB_KDB is not set (oops). * Better comment explaining why seq_file's lock member can be left uninitialized (its will not detect errors because we know it is already not allowed for seq_file ops to use it).
Daniel Thompson (3): kdb: Add framework to display sequence files proc: Provide access to /proc/interrupts from kdb kdb: Implement seq_file command
fs/proc/interrupts.c | 8 +++++++ include/linux/kdb.h | 5 +++++ kernel/debug/kdb/kdb_io.c | 53 +++++++++++++++++++++++++++++++++++++++++++++ kernel/debug/kdb/kdb_main.c | 28 ++++++++++++++++++++++++ 4 files changed, 94 insertions(+)