On Fri, 12 Nov 2021 06:12:11 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> wrote:
> Currently, the size of a trace buffer page is equal to the size of the
> system memory page. This may change in the future, so this assumption
> may not be valid. The proper way to determine the trace buffer page size
> is by using the information from "events/header_page" ftrace file:
> ...
> field: char data; offset:16; size:4080; signed:1;
> ...
> The trace buffer page size is the size of the "data" filed + its offset.
>
> A new libtraceevent API is introduced, for getting the trace buffer page
> size using that formula:
> tep_get_sub_buffer_size()
>
> Note, that some old kernels may not have "events/header_page" file. For
> those, the system memory page size is returned.
>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
> ---
>
> v2 changes:
> - Renamed tep_get_trace_page_size() to tep_get_sub_buffer_size().
> - Handle the old kernels in tep_parse_header_page() instead of in
> tep_get_sub_buffer_size().
>
> src/event-parse-api.c | 16 ++++++++++++++++
> src/event-parse.c | 2 ++
> src/event-parse.h | 1 +
> 3 files changed, 19 insertions(+)
>
> diff --git a/src/event-parse-api.c b/src/event-parse-api.c
> index f8361e4..f8433e5 100644
> --- a/src/event-parse-api.c
> +++ b/src/event-parse-api.c
> @@ -4,6 +4,7 @@
> *
> */
>
> +#include <unistd.h>
The above include isn't needed here anymore due to moving the
getpagesize into the C file.
-- Steve
> #include "event-parse.h"
> #include "event-parse-local.h"
> #include "event-utils.h"
> @@ -248,6 +249,21 @@ void tep_set_page_size(struct tep_handle *tep, int _page_size)
> tep->page_size = _page_size;
> }
>
> +/**
> + * tep_get_sub_buffer_size - get the size of a trace buffer page
> + * @tep: a handle to the tep_handle
> + *
> + * This returns the size of a trace buffer page on the traced machine.
> + * If @tep is NULL then -1 is returned.
> + */
> +int tep_get_sub_buffer_size(struct tep_handle *tep)
> +{
> + if (!tep)
> + return -1;
> +
> + return tep->header_page_data_size + tep->header_page_data_offset;
> +}
> +
> /**
> * tep_is_file_bigendian - return the endian of the file
> * @tep: a handle to the tep_handle
> diff --git a/src/event-parse.c b/src/event-parse.c
> index f42ae38..4b67289 100644
> --- a/src/event-parse.c
> +++ b/src/event-parse.c
> @@ -17,6 +17,7 @@
> #include <ctype.h>
> #include <errno.h>
> #include <stdint.h>
> +#include <unistd.h>
> #include <limits.h>
> #include <linux/time64.h>
>
> @@ -6905,6 +6906,7 @@ int tep_parse_header_page(struct tep_handle *tep, char *buf, unsigned long size,
> tep->header_page_ts_size = sizeof(long long);
> tep->header_page_size_size = long_size;
> tep->header_page_data_offset = sizeof(long long) + long_size;
> + tep->header_page_data_size = getpagesize() - tep->header_page_data_offset;
> tep->old_format = 1;
> return -1;
> }
> diff --git a/src/event-parse.h b/src/event-parse.h
> index d4a876f..e4ecde5 100644
> --- a/src/event-parse.h
> +++ b/src/event-parse.h
> @@ -565,6 +565,7 @@ void tep_set_cpus(struct tep_handle *tep, int cpus);
> int tep_get_long_size(struct tep_handle *tep);
> void tep_set_long_size(struct tep_handle *tep, int long_size);
> int tep_get_page_size(struct tep_handle *tep);
> +int tep_get_sub_buffer_size(struct tep_handle *tep);
> void tep_set_page_size(struct tep_handle *tep, int _page_size);
> bool tep_is_file_bigendian(struct tep_handle *tep);
> void tep_set_file_bigendian(struct tep_handle *tep, enum tep_endian endian);
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