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baa031b7bd
Allow more than one field of a syscall trace event to read user space. Build on top of the user_mask by allowing more than one bit to be set that corresponds to the @args array of the syscall metadata. For each argument in the @args array that is to be read, it will have a dynamic array/string field associated to it. Note that multiple fields to be read from user space is not supported if the user_arg_size field is set in the syscall metada. That field can only be used if only one field is being read from user space as that field is a number representing the size field of the syscall event that holds the size of the data to read from user space. It becomes ambiguous if the system call reads more than one field. Currently this is not an issue. If a syscall event happens to enable two events to read user space and sets the user_arg_size field, it will trigger a warning at boot and the user_arg_size field will be cleared. The per CPU buffer that is used to read the user space addresses is now broken up into 3 sections, each of 168 bytes. The reason for 168 is that it is the biggest portion of 512 bytes divided by 3 that is 8 byte aligned. The max amount copied into the ring buffer from user space is now only 128 bytes, which is plenty. When reading user space, it still reads 167 (168-1) bytes and uses the remaining to know if it should append the extra "..." to the end or not. This will allow the event to look like this: sys_renameat2(olddfd: 0xffffff9c, oldname: 0x7ffe02facdff "/tmp/x", newdfd: 0xffffff9c, newname: 0x7ffe02face06 "/tmp/y", flags: 1) Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Takaya Saeki <takayas@google.com> Cc: Tom Zanussi <zanussi@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ian Rogers <irogers@google.com> Cc: Douglas Raillard <douglas.raillard@arm.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Ingo Molnar <mingo@redhat.com> Link: https://lore.kernel.org/20251028231148.095789277@kernel.org Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
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.