tools/opensnoop: Display mode for -e, --extended_fields

[Rtoax]

When a program creates a file with mode=0000, it cannot even access the file
itself. It would be helpful if we could track the mode value. so we can know
who did it.

Example:

    open("a.txt", O_WRONLY | O_EXCL | O_CREAT, 0000);

Then:

    $ ls -l a.txt
    ----------. 1 rongtao rongtao 0 Jan 24 09:07 a.txt
    $ cat a.txt
    cat: a.txt: Permission denied

    $ sudo ./opensnoop.py -e
    PID    COMM               FD ERR FLAGS    MODE PATH
    673067 open                3   0 00000301 0000 a.txt
                                              ^^^^

[ekyooo]

Could you include in the commit message when it is useful to output MODE information, which can be verified outside of the tool, within the tool itself?

[Rtoax]

Could you include in the commit message when it is useful to output MODE information, which can be verified outside of the tool, within the tool itself?

Thanks, I just add the extra information.

[Rtoax]

Rebase to master

[yonghong-song]

Although for struct open_how, it uses __u64 for flags and mode, but
in reality, mode value should be still within 32bit range.

So I suggest to change 'mode' type to __u32 (unsigned int) instead of 'unsigned short'.