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Diffstat (limited to 'Documentation/dynamic-debug-howto.txt')
| -rw-r--r-- | Documentation/dynamic-debug-howto.txt | 26 |
1 files changed, 23 insertions, 3 deletions
diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt index 6e1684981da..9417871b875 100644 --- a/Documentation/dynamic-debug-howto.txt +++ b/Documentation/dynamic-debug-howto.txt @@ -6,8 +6,16 @@ This document describes how to use the dynamic debug (dyndbg) feature. Dynamic debug is designed to allow you to dynamically enable/disable kernel code to obtain additional kernel information. Currently, if -CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() calls can -be dynamically enabled per-callsite. +CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() and +print_hex_dump_debug()/print_hex_dump_bytes() calls can be dynamically +enabled per-callsite. + +If CONFIG_DYNAMIC_DEBUG is not set, print_hex_dump_debug() is just +shortcut for print_hex_dump(KERN_DEBUG). + +For print_hex_dump_debug()/print_hex_dump_bytes(), format string is +its 'prefix_str' argument, if it is constant string; or "hexdump" +in case 'prefix_str' is build dynamically. Dynamic debug has even more useful features: @@ -100,6 +108,12 @@ If your query set is big, you can batch them too: ~# cat query-batch-file > <debugfs>/dynamic_debug/control +A another way is to use wildcard. The match rule support '*' (matches +zero or more characters) and '?' (matches exactly one character).For +example, you can match all usb drivers: + + ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control + At the syntactical level, a command comprises a sequence of match specifications, followed by a flags change specification. @@ -202,6 +216,9 @@ The flags are: t Include thread ID in messages not generated from interrupt context _ No flags are set. (Or'd with others on input) +For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag +have meaning, other flags ignored. + For display, the flags are preceded by '=' (mnemonic: what the flags are currently equal to). @@ -268,7 +285,7 @@ The dyndbg option is a "fake" module parameter, which means: - modules do not need to define it explicitly - every module gets it tacitly, whether they use pr_debug or not -- it doesnt appear in /sys/module/$module/parameters/ +- it doesn't appear in /sys/module/$module/parameters/ To see it, grep the control file, or inspect /proc/cmdline. For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or @@ -304,6 +321,9 @@ nullarbor:~ # echo -n 'func svc_process -p' > nullarbor:~ # echo -n 'format "nfsd: READ" +p' > <debugfs>/dynamic_debug/control +// enable messages in files of which the paths include string "usb" +nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control + // enable all messages nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control |