[PATCH] netlink: decode libudev netlink header

[Chen Jingpiao]

On Wed, 3 Jan 2018 18:33:46 +0530, Harsha Sharma wrote:
> * netlink.c: decode family NETLINK_KOBJECT_UEVENT if prefix is libudev
> * linux/netlink_kobject_uevent.h: New struct (udev_monitor_netlink_header)

I think this header should not in linux directory.
When adding a new file, we should add it in Makefile.am.

>
> Signed-off-by: Harsha Sharma <harshasharmaiitr at gmail.com>
> ---
>  linux/netlink_kobject_uevent.h | 16 ++++++++++++++++
>  netlink.c                      | 27 ++++++++++++++++++++++++++-
>  2 files changed, 42 insertions(+), 1 deletion(-)
>  create mode 100644 linux/netlink_kobject_uevent.h
>
> diff --git a/linux/netlink_kobject_uevent.h
b/linux/netlink_kobject_uevent.h
> new file mode 100644
> index 00000000..d83ccad5
> --- /dev/null
> +++ b/linux/netlink_kobject_uevent.h
> @@ -0,0 +1,16 @@
> +#ifndef STRACE_LINUX_NETLINK_KOBJECT_UEVENT_H
> +#define STRACE_LINUX_NETLINK_KOBJECT_UEVENT_H
> +
> +struct udev_monitor_netlink_header {
> + char prefix[8];

Reserve useful comment.

> + unsigned int magic;
> + unsigned int header_size;
> + unsigned int properties_off;
> + unsigned int properties_len;
> + unsigned int filter_subsystem_hash;
> + unsigned int filter_devtype_hash;
> + unsigned int filter_tag_bloom_hi;
> + unsigned int filter_tag_bloom_lo;
> +};
> +
> +#endif /* !STRACE_LINUX_NETLINK_KOBJECT_UEVENT_H */
> diff --git a/netlink.c b/netlink.c
> index 6b9a1f5c..e991ed86 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -32,6 +32,7 @@
>  #include "nlattr.h"
>  #include <linux/audit.h>
>  #include <linux/rtnetlink.h>
> +#include <linux/netlink_kobject_uevent.h>
>  #include <linux/xfrm.h>
>  #include "xlat/netlink_ack_flags.h"
>  #include "xlat/netlink_delete_flags.h"
> @@ -183,6 +184,29 @@ decode_nlmsg_type_netfilter(const struct xlat *const
xlat,
>   tprintf("%#x", msg_type);
>  }
>
> +static bool
> +decode_nlmsg_type_kobject_uevent(struct tcb *tcp, kernel_ulong_t addr,
> + kernel_ulong_t len,
> + const void *const opaque_data)
> +{
> + struct udev_monitor_netlink_header uh;
> + const char *prefix = "libudev";
> +
> + if (len < sizeof(uh))
> + return false;
> + if (!umove_or_printaddr(tcp, addr, &uh) &&
> +    strcmp(uh.prefix, prefix) == 0) {
> + tprintf("{prefix=%s, magic=%u, header_size=%u, properties_off=%u,
properties_len=%u, filter_subsystem_hash=%u, filter_devtype_hash=%u,
filter_tag_bloom_hi=%u, filter_tag_bloom_lo=%u}", uh.prefix,

More than 80 character.

> +    uh.magic, uh.header_size, uh.properties_off,
> +    uh.properties_len, uh.filter_subsystem_hash,
> +    uh.filter_devtype_hash, uh.filter_tag_bloom_hi,
> +    uh.filter_tag_bloom_lo);

We can use macros in print_fields.h.
I think magic, filter_tag_bloom_hi and filter_tag_bloom_lo sholud use other
format.

After the header have other messages.

> + return true;
> + }
> + return false;

If umove_or_printaddr return -1, you print address and string.
If prefix is not "libudev", address addr to (addr + sizeof(uh)) will call
umove
again, we should reduce call syscall.

> +}

I think this function should separate into a single file.

> +
> +

To more empty line.

>  typedef void (*nlmsg_types_decoder_t)(const struct xlat *,
>        uint16_t type,
>        const char *dflt);
> @@ -628,7 +652,8 @@ decode_netlink(struct tcb *const tcp,
>   const int family = get_fd_nl_family(tcp, fd);
>
>   if (family == NETLINK_KOBJECT_UEVENT) {
> - printstrn(tcp, addr, len);
> + if (!decode_nlmsg_type_kobject_uevent(tcp, addr, len, NULL))

I think this should be named decode_netlink_kobject_uevent, then ...

> + printstrn(tcp, addr, len);

... this problem handle in this function.

if (family == NETLINK_KOBJECT_UEVENT) {
decode_netlink_kobject_uevent(tcp, addr, len);
return;
}

>   return;
>   }
>
> --
> 2.11.0
>

Without a test.

--
Chen Jingpiao
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