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    SubjectRe: [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape_mem
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    On Mon, Feb 23 2015, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

    >> >> > So, why couldn't we split this to separate test case? It seems I already
    >> >> > pointed this out.
    >> >> >
    >> >>
    >> >> This actually provides better coverage
    >> >
    >> > I do not see much advantage of doing so. You may create a loop with
    >> > random number for in-size and check. So, I prefer to see separate case
    >> > for that.
    >>
    >> It's not about the size, it's about exercising all the various escape_*
    >> helpers, to ensure that they all respect the end of the buffer, while
    >> still returning the correct would-be output size. For that, one needs to
    >> call string_escape_mem with various combinations of flags and input
    >> buffers. The logic for that is already in place in test_string_escape
    >> and its caller, and I see no point in duplicating all that.
    >
    > Thanks for clarification.
    >
    >> If you insist on a separate function for doing the overflow testing,
    >> I'll just rip it out from my code and let you add such a test later.
    >
    > What about to make it a separate function *and* call from inside of
    > test_string_escape? Would it work for you?

    See my earlier point about "quite a lot of state to pass". But if this

    static __init void
    test_string_escape_overflow(const char *in, int p, char *out_real, int out_size,
    unsigned int flags, const char *esc, int q_test,
    const char *name)
    {
    int q_real;

    memset(out_real, 'Z', out_size);
    q_real = string_escape_mem(in, p, out_real, 0, flags, esc);
    if (q_real != q_test)
    pr_warn("Test '%s' failed: flags = %u, osz = 0, expected %d, got %d\n",
    name, flags, q_test, q_real);
    if (memchr_inv(out_real, 'Z', out_size))
    pr_warn("Test '%s' failed: osz = 0 but string_escape_mem wrote to the buffer\n",
    name);
    }

    is what you want, sure, have it your way.

    I need to fix fs/proc/array.c in 3/3 as well, to make the kernel
    compile+boot and make the series bisectable. Before I send v4 please let
    me know what you think about this (the minimal fix I could come up with):

    diff --git a/fs/proc/array.c b/fs/proc/array.c
    index 1295a00ca316..20f2d50e2dba 100644
    --- a/fs/proc/array.c
    +++ b/fs/proc/array.c
    @@ -99,10 +99,9 @@ static inline void task_name(struct seq_file *m, struct task_struct *p)
    buf = m->buf + m->count;

    /* Ignore error for now */
    - string_escape_str(tcomm, &buf, m->size - m->count,
    - ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\");
    + m->count += string_escape_str(tcomm, buf, m->size - m->count,
    + ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\");

    - m->count = buf - m->buf;
    seq_putc(m, '\n');
    }

    [Longer-term I think it would be a lot better not to poke around in
    the internals of struct seq_file. One way is to do the escaping into a
    stack buffer (2*sizeof(p->comm) should be enough) and then use something
    like seq_write(m, buffer, min(sizeof(buffer),
    return-value-from-string_escape_str)).
    Another option is to do everything with a single seq_printf call,
    something like

    seq_printf(m, "Name:\t%*pEcs\n, (int)strlen(tcomm), tcomm)

    That will escape more than just \ and \n, but that would IMO be an
    improvement. But of course this is out of scope for this series.]

    Rasmus


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