linux-kernel - Re: [PATCH v5 16/18] perf: enable reading of perf.data files from different ABI rev

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Message-ID: <20120206182208.GH6367@infradead.org>
Date:	Mon, 6 Feb 2012 16:22:08 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	robert.richter@....com, ming.m.lin@...el.com, andi@...stfloor.org,
	asharma@...com, ravitillo@....gov, vweaver1@...s.utk.edu,
	khandual@...ux.vnet.ibm.com, dsahern@...il.com
Subject: Re: [PATCH v5 16/18] perf: enable reading of perf.data files from
	different ABI rev

Em Thu, Feb 02, 2012 at 01:54:46PM +0100, Stephane Eranian escreveu:
> This patch allows perf to process perf.data files generated
> using an ABI that has a different perf_event_attr struct size, i.e.,
> a different ABI version.
> 
> The perf_event_attr can be extended, yet perf needs to cope with
> older perf.data files. Similarly, perf must be able to cope with
> a perf.data file which is using a newer version of the ABI than
> what it knows about.
> 
> This patch adds read_attr(), a routine that reads a perf_event_attr
> struct from a file incrementally based on its advertised size. If
> the on-file struct is smaller than what perf knows, then the extra
> fields are zeroed. If the on-file struct is bigger, then perf only
> uses what it knows about, the rest is skipped.

Anshuman, can I have your Acked-by or Reviewed-by since you spotted
problems in this and your suggestions were taken into account? Is this
OK now?

- Arnaldo
 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  tools/perf/util/header.c |   49 ++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 6f4187d..8d6c18d 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1959,6 +1959,51 @@ static int perf_header__read_pipe(struct perf_session *session, int fd)
>  	return 0;
>  }
>  
> +static int read_attr(int fd, struct perf_header *ph,
> +		     struct perf_file_attr *f_attr)
> +{
> +	struct perf_event_attr *attr = &f_attr->attr;
> +	size_t sz, left;
> +	size_t our_sz = sizeof(f_attr->attr);
> +	int ret;
> +
> +	memset(f_attr, 0, sizeof(*f_attr));
> +
> +	/* read minimal guaranteed structure */
> +	ret = readn(fd, attr, PERF_ATTR_SIZE_VER0);
> +	if (ret <= 0)
> +		return -1;
> +
> +	/* on file perf_event_attr size */
> +	sz = attr->size;
> +	if (ph->needs_swap)
> +		sz = bswap_32(sz);
> +
> +	if (sz == 0) {
> +		/* assume ABI0 */
> +		sz =  PERF_ATTR_SIZE_VER0;
> +	} else if (sz > our_sz) {
> +		/* bigger than what we know about */
> +		sz = our_sz;
> +
> +		/* skip what we do not know about */
> +		lseek(fd, SEEK_CUR, attr->size - our_sz);
> +	}
> +	/* what we have not yet read and that we know about */
> +	left = sz - PERF_ATTR_SIZE_VER0;
> +	if (left) {
> +		void *ptr = attr;
> +		ptr += PERF_ATTR_SIZE_VER0;
> +
> +		ret = readn(fd, ptr, left);
> +		if (ret <= 0)
> +			return -1;
> +	}
> +	/* read the ids */
> +	ret = readn(fd, &f_attr->ids, sizeof(struct perf_file_section));
> +	return ret <= 0 ? -1 : 0;
> +}
> +
>  int perf_session__read_header(struct perf_session *session, int fd)
>  {
>  	struct perf_header *header = &session->header;
> @@ -1979,14 +2024,14 @@ int perf_session__read_header(struct perf_session *session, int fd)
>  		return -EINVAL;
>  	}
>  
> -	nr_attrs = f_header.attrs.size / sizeof(f_attr);
> +	nr_attrs = f_header.attrs.size / f_header.attr_size;
>  	lseek(fd, f_header.attrs.offset, SEEK_SET);
>  
>  	for (i = 0; i < nr_attrs; i++) {
>  		struct perf_evsel *evsel;
>  		off_t tmp;
>  
> -		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
> +		if (read_attr(fd, header, &f_attr) < 0)
>  			goto out_errno;
>  
>  		if (header->needs_swap)
> -- 
> 1.7.4.1
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