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If all functions are enabled, there's a comment displayed in the file to denote that: # cd /sys/kernel/debug/tracing # cat set_ftrace_filter #### all functions enabled #### If a function trigger is set, those are displayed as well: # echo schedule:traceoff >> /debug/tracing/set_ftrace_filter # cat set_ftrace_filter #### all functions enabled #### schedule:traceoff:unlimited But if you read that file with dd, the output can change: # dd if=/debug/tracing/set_ftrace_filter bs=1 #### all functions enabled #### 32+0 records in 32+0 records out 32 bytes copied, 7.0237e-05 s, 456 kB/s This is because the "pos" variable is updated for the comment, but func_pos is not. "func_pos" is used by the triggers (or hashes) to know how many functions were printed and it bases its index from the pos - func_pos. func_pos should be 1 to count for the comment printed. But since it is not, t_hash_start() thinks that one trigger was already printed. The cat gets to t_hash_start() via t_next() and not t_start() which updates both pos and func_pos. Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.