Re: Benchmarked tcpserver dlopen() -> qmail_smtpd() VS tcpserver --> fork() --> exec qmail-smtpd

On 4 April 2017 at 23:12, Charles Cazabon
<[email protected]> wrote:
> Manvendra Bhangui <[email protected]> wrote:
>> badmailfrom, there is a huge difference. In the case of indimail-mta,
>> I loaded 50 Mib of control file.
>
> And what was your control-file read buffer size?  64 bytes?  That's nearly
> 800,000 syscalls just to read the bloody file.  No wonder you think it's slow.
>

static char     inbuf[64];

.....
buffer_init(&ss, read, fd, inbuf, sizeof inbuf);

BTW I don't use such huge files without using cdb or using MySQL. The
control.c which I have already uses .cdb if the control file name has
.cdb extension and MySQL if the file has .sql extension. The point I
am trying to make is that in the dlopen() method, I load the control
file just once in the lifetime - Just once. The crazy 25 MiB control
file was just an experiment. Even in the normal scenario where the
control files are just few KiB, I am seeing a very small performance
gain. I have the code read, working and tested. It is just that I am
struggling to make the tcpserver symbols private. Yesterday I
discovered that one can make the namespace private by using dlmopen()
call instead of dlopen(). However, I have been struggling to make
dlmopen() work with tcpserver. The tcpserver goes into consuming 100%
cpu. With the help of gdb, I have just figured out the reason. The
culprit is prot_uid() and prot_gid() functions in tcpserver. They use
int data type for uid and gid. The moment I call setgid(), setgroups()
or setuid(), these calls do not return and goes into an infinite loop.
It is a situation like errno.h. I need to change the data type for uid
and gid to uid_t and gid_t as they are defined in sys/types.h. If I do
that, tcpserver is working perfectly and securely without its
namespace exposed to other externally loaded library and hence as safe
as execv().

I think this could be a bug with dlmopen() or the kernel that I have
uncovered. Even strace stops working as soon as setuid(), setgid() or
setgroups() gets called, with an error
strace: process runs in x32 mode

This entire exercise has been an academic exercise and an attempt to
learn about how the unix loader works
Cheers :)
and even as I write this, I think I have figured out the