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updates the documentation for 'dynamic debug' feature. Signed-off-by: Greg Banks <[email protected]> Signed-off-by: Jason Baron <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
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| Introduction | ||
| ============ | ||
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| This document describes how to use the dynamic debug (ddebug) feature. | ||
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| 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_debug() calls can be | ||
| dynamically enabled per-callsite. | ||
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| Dynamic debug has even more useful features: | ||
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| * Simple query language allows turning on and off debugging statements by | ||
| matching any combination of: | ||
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| - source filename | ||
| - function name | ||
| - line number (including ranges of line numbers) | ||
| - module name | ||
| - format string | ||
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| * Provides a debugfs control file: <debugfs>/dynamic_debug/control which can be | ||
| read to display the complete list of known debug statements, to help guide you | ||
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| Controlling dynamic debug Behaviour | ||
| =============================== | ||
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| The behaviour of pr_debug()/dev_debug()s are controlled via writing to a | ||
| control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs | ||
| filesystem, in order to make use of this feature. Subsequently, we refer to the | ||
| control file as: <debugfs>/dynamic_debug/control. For example, if you want to | ||
| enable printing from source file 'svcsock.c', line 1603 you simply do: | ||
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| nullarbor:~ # echo 'file svcsock.c line 1603 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| If you make a mistake with the syntax, the write will fail thus: | ||
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| nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
| -bash: echo: write error: Invalid argument | ||
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| Viewing Dynamic Debug Behaviour | ||
| =========================== | ||
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| You can view the currently configured behaviour of all the debug statements | ||
| via: | ||
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| nullarbor:~ # cat <debugfs>/dynamic_debug/control | ||
| # filename:lineno [module]function flags format | ||
| /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup - "SVCRDMA\040Module\040Removed,\040deregister\040RPC\040RDMA\040transport\012" | ||
| /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline\040\040\040\040\040\040\040:\040%d\012" | ||
| /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth\040\040\040\040\040\040\040\040\040:\040%d\012" | ||
| /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests\040\040\040\040\040:\040%d\012" | ||
| ... | ||
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| You can also apply standard Unix text manipulation filters to this | ||
| data, e.g. | ||
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| nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l | ||
| 62 | ||
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| nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l | ||
| 42 | ||
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| Note in particular that the third column shows the enabled behaviour | ||
| flags for each debug statement callsite (see below for definitions of the | ||
| flags). The default value, no extra behaviour enabled, is "-". So | ||
| you can view all the debug statement callsites with any non-default flags: | ||
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| nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control | ||
| # filename:lineno [module]function flags format | ||
| /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process:\040st_sendto\040returned\040%d\012" | ||
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| Command Language Reference | ||
| ========================== | ||
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| At the lexical level, a command comprises a sequence of words separated | ||
| by whitespace characters. Note that newlines are treated as word | ||
| separators and do *not* end a command or allow multiple commands to | ||
| be done together. So these are all equivalent: | ||
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| nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
| nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' > | ||
| <debugfs>/dynamic_debug/control | ||
| nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
| nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| Commands are bounded by a write() system call. If you want to do | ||
| multiple commands you need to do a separate "echo" for each, like: | ||
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| nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\ | ||
| > echo 'file svcsock.c line 1563 +p' > /proc/dprintk | ||
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| or even like: | ||
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| nullarbor:~ # ( | ||
| > echo 'file svcsock.c line 1603 +p' ;\ | ||
| > echo 'file svcsock.c line 1563 +p' ;\ | ||
| > ) > /proc/dprintk | ||
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| At the syntactical level, a command comprises a sequence of match | ||
| specifications, followed by a flags change specification. | ||
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| command ::= match-spec* flags-spec | ||
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| The match-spec's are used to choose a subset of the known dprintk() | ||
| callsites to which to apply the flags-spec. Think of them as a query | ||
| with implicit ANDs between each pair. Note that an empty list of | ||
| match-specs is possible, but is not very useful because it will not | ||
| match any debug statement callsites. | ||
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| A match specification comprises a keyword, which controls the attribute | ||
| of the callsite to be compared, and a value to compare against. Possible | ||
| keywords are: | ||
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| match-spec ::= 'func' string | | ||
| 'file' string | | ||
| 'module' string | | ||
| 'format' string | | ||
| 'line' line-range | ||
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| line-range ::= lineno | | ||
| '-'lineno | | ||
| lineno'-' | | ||
| lineno'-'lineno | ||
| // Note: line-range cannot contain space, e.g. | ||
| // "1-30" is valid range but "1 - 30" is not. | ||
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| lineno ::= unsigned-int | ||
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| The meanings of each keyword are: | ||
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| func | ||
| The given string is compared against the function name | ||
| of each callsite. Example: | ||
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| func svc_tcp_accept | ||
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| file | ||
| The given string is compared against either the full | ||
| pathname or the basename of the source file of each | ||
| callsite. Examples: | ||
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| file svcsock.c | ||
| file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c | ||
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| module | ||
| The given string is compared against the module name | ||
| of each callsite. The module name is the string as | ||
| seen in "lsmod", i.e. without the directory or the .ko | ||
| suffix and with '-' changed to '_'. Examples: | ||
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| module sunrpc | ||
| module nfsd | ||
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| format | ||
| The given string is searched for in the dynamic debug format | ||
| string. Note that the string does not need to match the | ||
| entire format, only some part. Whitespace and other | ||
| special characters can be escaped using C octal character | ||
| escape \ooo notation, e.g. the space character is \040. | ||
| Examples: | ||
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| format svcrdma: // many of the NFS/RDMA server dprintks | ||
| format readahead // some dprintks in the readahead cache | ||
| format nfsd:\040SETATTR // how to match a format with whitespace | ||
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| line | ||
| The given line number or range of line numbers is compared | ||
| against the line number of each dprintk() callsite. A single | ||
| line number matches the callsite line number exactly. A | ||
| range of line numbers matches any callsite between the first | ||
| and last line number inclusive. An empty first number means | ||
| the first line in the file, an empty line number means the | ||
| last number in the file. Examples: | ||
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| line 1603 // exactly line 1603 | ||
| line 1600-1605 // the six lines from line 1600 to line 1605 | ||
| line -1605 // the 1605 lines from line 1 to line 1605 | ||
| line 1600- // all lines from line 1600 to the end of the file | ||
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| The flags specification comprises a change operation followed | ||
| by one or more flag characters. The change operation is one | ||
| of the characters: | ||
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| - | ||
| remove the given flags | ||
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| + | ||
| add the given flags | ||
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| = | ||
| set the flags to the given flags | ||
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| The flags are: | ||
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| p | ||
| Causes a printk() message to be emitted to dmesg | ||
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| Note the regexp ^[-+=][scp]+$ matches a flags specification. | ||
| Note also that there is no convenient syntax to remove all | ||
| the flags at once, you need to use "-psc". | ||
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| Examples | ||
| ======== | ||
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| // enable the message at line 1603 of file svcsock.c | ||
| nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| // enable all the messages in file svcsock.c | ||
| nullarbor:~ # echo -n 'file svcsock.c +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| // enable all the messages in the NFS server module | ||
| nullarbor:~ # echo -n 'module nfsd +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| // enable all 12 messages in the function svc_process() | ||
| nullarbor:~ # echo -n 'func svc_process +p' > | ||
| <debugfs>/dynamic_debug/control | ||
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| // disable all 12 messages in the function svc_process() | ||
| nullarbor:~ # echo -n 'func svc_process -p' > | ||
| <debugfs>/dynamic_debug/control |
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