[RFC 2/4] Add eventfd option to --decode-fds

[Masatake YAMATO]

Hi,

From: Sahil Siddiq <icegambit91 at gmail.com>
Subject: [RFC 2/4] Add eventfd option to --decode-fds
Date: Mon, 29 Apr 2024 09:01:45 +0530

> Having an eventfd option for --decode-fds will help
> examine the eventfd counter associated with an eventfd
> file descriptor.
> 
> * src/filter_qualify.c
>   (decode_fd_str_to_uint): Add "eventfd" option.
>   (parse_inject_token): Pass base 10 as argument.
> * src/number_set.h: Add DECODE_FD_EVENTFD.
> * src/strace.c: Add "eventfd" option.
> * src/util.c: Parse eventfd counter value.
> 
> Signed-off-by: Sahil Siddiq <icegambit91 at gmail.com>
> ---
>  src/filter_qualify.c |  5 +++--
>  src/number_set.h     |  1 +
>  src/strace.c         |  3 ++-
>  src/util.c           | 37 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/src/filter_qualify.c b/src/filter_qualify.c
> index be383a5c9..a79045468 100644
> --- a/src/filter_qualify.c
> +++ b/src/filter_qualify.c
> @@ -105,6 +105,7 @@ decode_fd_str_to_uint(const char *str)
>  		{ DECODE_FD_PATH,      "path" },
>  		{ DECODE_FD_SOCKET,    "socket" },
>  		{ DECODE_FD_DEV,       "dev" },
> +		{ DECODE_FD_EVENTFD,   "eventfd" },
>  		{ DECODE_FD_PIDFD,     "pidfd" },
>  		{ DECODE_FD_SIGNALFD,  "signalfd" },
>  	};
> @@ -273,7 +274,7 @@ parse_inject_token(const char *const token, struct inject_opts *const fopts,
>  		 * F..L+S
>  		 */
>  		char *end;
> -		intval = string_to_uint_ex(val, &end, 0xffff, "+.");
> +		intval = string_to_uint_ex(val, &end, 0xffff, "+.", 10);
>  		if (intval < 1)
>  			return false;
>  
> @@ -287,7 +288,7 @@ parse_inject_token(const char *const token, struct inject_opts *const fopts,
>  			 * F..L+S
>  			 */
>  			val = end + 2;
> -			intval = string_to_uint_ex(val, &end, 0xffff, "+");
> +			intval = string_to_uint_ex(val, &end, 0xffff, "+", 10);
>  			if (intval < fopts->first || intval == INJECT_LAST_INF)
>  				return false;
>  			fopts->last = intval;
> diff --git a/src/number_set.h b/src/number_set.h
> index 0ce2b2db6..d28ac0cdd 100644
> --- a/src/number_set.h
> +++ b/src/number_set.h
> @@ -75,6 +75,7 @@ enum decode_fd_bits {
>  	DECODE_FD_PATH,
>  	DECODE_FD_SOCKET,
>  	DECODE_FD_DEV,
> +	DECODE_FD_EVENTFD,
>  	DECODE_FD_PIDFD,
>  	DECODE_FD_SIGNALFD,
>  
> diff --git a/src/strace.c b/src/strace.c
> index c8f76cada..a5f87c3bb 100644
> --- a/src/strace.c
> +++ b/src/strace.c
> @@ -378,7 +378,8 @@ Output format:\n\
>                   print exit reason of kvm vcpu\n\
>    -e decode-fds=SET, --decode-fds=SET\n\
>                   what kinds of file descriptor information details to decode\n\
> -     details:    dev (device major/minor for block/char device files)\n\
> +     details:    dev (device major/minor for block/char device files),\n\
> +                 eventfd (associated eventfd counter for eventfds),\n\
>                   path (file path),\n\
>                   pidfd (associated PID for pidfds),\n\
>                   socket (protocol-specific information for socket descriptors),\n\
> diff --git a/src/util.c b/src/util.c
> index 4140cb718..edcdf440c 100644
> --- a/src/util.c
> +++ b/src/util.c
> @@ -858,6 +858,40 @@ printsignalfd(pid_t pid_of_fd, int fd, const char *path)
>  			   print_fdinfo_sigmask, NULL);
>  }
>  
> +static bool
> +parse_fdinfo_efd_counter(const char *value, void *data)
> +{	uint64_t *efd_counter = data;
> +	*efd_counter = string_to_uint_ex(value, NULL, ULLONG_MAX, "\n", 16);
> +	return true;
> +}
> +
> +static bool
> +printeventfd(pid_t pid_of_fd, int fd, const char *path)
> +{
> +	static const char eventfd_path[] = "anon_inode:[eventfd]";
> +	static const char efd_counter_pfx[] = "eventfd-count:";

In addition to "count", I think printing "id" is useful.

    $ cat /proc/56214/fdinfo/42
    pos:	0
    flags:	02004002
    mnt_id:	16
    ino:	72
    eventfd-count:                0
    eventfd-id: 114
    eventfd-semaphore: 0

All eventfds have the same inode number.  On the other hand
eventfd-id can be used to identify eventfd instances.
See https://patchwork.kernel.org/project/linux-fsdevel/patch/20180520201823.14293-1-yamato@redhat.com/

I expect strace repots the above example as

	   42<eventfd count:0 id:114">


> +	if (strcmp(path, eventfd_path))
> +		return false;
> +
> +	uint64_t efd_counter = -1ULL;
> +
> +	scan_fdinfo(pid_of_fd, fd, efd_counter_pfx, sizeof(efd_counter_pfx) - 1,
> +			   parse_fdinfo_efd_counter, &efd_counter);
> +
> +	if (efd_counter != -1ULL) {
> +		tprint_associated_info_begin();
> +		tprints_string("eventfd-count:");
> +		PRINT_VAL_U(efd_counter);
> +		tprint_associated_info_end();
> +	} else {
> +		;
> +		// print_string_in_angle_brackets(path);
> +	}
> +
> +	return true;
> +}
> +
>  static void
>  print_quoted_string_in_angle_brackets(const char *str, const bool deleted)
>  {
> @@ -886,6 +920,9 @@ printfd_pid_with_finfo(struct tcb *tcp, pid_t pid, int fd, const struct finfo *f
>  		if (is_number_in_set(DECODE_FD_DEV, decode_fd_set) &&
>  		    printdev(tcp, fd, path, finfo))
>  			goto printed;
> +		if (is_number_in_set(DECODE_FD_EVENTFD, decode_fd_set) &&
> +		    printeventfd(pid, fd, path))
> +			goto printed;
>  		if (is_number_in_set(DECODE_FD_PIDFD, decode_fd_set) &&
>  		    printpidfd(pid, fd, path))
>  			goto printed;
> -- 
> 2.44.0
> 
> -- 
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> 

Masatake YAMATO