problem in programming with inotify

shifter · 03-28-2007, 07:25 PM

Hello all, I would like to develop a pplication with inotify.
Now my code is stupid, but it does yet error.
When I try 'gcc myprogram.c -o myprogram' the output is:

/tmp/ccef8sAa.o(.text+0x1d): In function 'main':
:undefined reference to 'inotify_init'
collect2: ld retuned 1 exit status

It seems that it don't find inotify_init. I tried 'grep INOTIFY /boot/config' and output is:

CONFIG_INOTIFY=y
CONFIG_INOTIFY_USER=y

The command 'man inotify_init' return man page of above syscall.

What is the problem?
Is there someone that it can help me?

Thanks in advance,
Shift

osor · 03-28-2007, 07:30 PM

What version of glibc do you have?
Was it compiled with inotify support?

shifter · 03-28-2007, 08:00 PM

Quote:

What version of glibc do you have?

I have a Slackware 11, then I suppose that I am using glibc-2.3.6.
Inotify.h did not present in /usr/include/sys, but I copied inotify.h from /usr/src/linux/fs

Quote:

Was it compiled with inotify support?

No, but I installed a precompiled kernel 2.6.18 provided with distribution (test26.s)

osor · 03-28-2007, 08:44 PM

Quote:

Originally Posted by shifter

No, but I installed a precompiled kernel 2.6.18 provided with distribution (test26.s)

If such is the case (i.e., your glibc has no built-in inotify support), you need to use the system calls directly. Your originally posted problem is a linking one and thus can be fixed if you identify your own inotify functions wrapping the linux system calls. E.g. (from inotify-syscalls.h):

Code:

#include <sys/syscall.h>

static inline int inotify_init (void)
{
	return syscall (__NR_inotify_init);
}

static inline int inotify_add_watch (int fd, const char *name, __u32 mask)
{
	return syscall (__NR_inotify_add_watch, fd, name, mask);
}

static inline int inotify_rm_watch (int fd, __u32 wd)
{
	return syscall (__NR_inotify_rm_watch, fd, wd);
}

And voila… no more undefined references.

shifter · 03-28-2007, 08:50 PM

What are steps that I need to do exactly?
What I must add to code?

Thanks

osor · 03-28-2007, 09:26 PM

Quote:

Originally Posted by shifter

What are steps that I need to do exactly?
What I must add to code?

Thanks

You have a few options:

If you have a the file <sys/inotify-syscalls.h> in your include path, just include that file at the beginning of each source file you need it in.
Make your own inotify-syscalls.h header with the lines of the previous post (of course you need to surround the code with #ifndef _LINUX_INOTIFY_SYSCALLS_H\
#define _LINUX_INOTIFY_SYSCALLS_H at the beginning and #endif at the end as is custom with C header files). Include it at the beginning of each source file you need it in.
Put the lines from the previous post at the beginning of each source file you need it in.

The important thing is to have the definitions of the wrapper functions (which will most likely be inlined anyway) visible to the rest of source, so they are not assumed by the compiler to reside in an external library (e.g., glibc), and so that the linker does not complain when they are not found in the aforementioned library.

Also, you might want to take a look at this (though it’s a bit old).

gjo · 03-30-2007, 05:28 AM

sorry,it was a wrong thread...

osor · 03-30-2007, 08:32 AM

Are you sure you posted the above post in the correct thread?

shifter · 04-01-2007, 09:17 PM

Exactly, what is __u32 in inotify?
The event->mask field in declared as __u32.
How can I to compare __u32 with an integer? for example '__u32 == IN_ACCESS'

Thanks in advance to help.

shifter · 04-01-2007, 10:42 PM

Now my problem is the following:

if (event->mask & IN_ISDIR) printf("IS A DIRECTORY");

but gcc outputs 'error: dereferencing pointer to incomplete type'.
Now what is the problem????
I am despaired...

osor · 04-02-2007, 12:46 PM

Quote:

Originally Posted by shifter

Exactly, what is __u32 in inotify?
The event->mask field in declared as __u32.
How can I to compare __u32 with an integer? for example '__u32 == IN_ACCESS'

Thanks in advance to help.

In case you did’t figure it out yet, __u32 is an unsigned 32-bit integer storage unit. It can be compared with a literal numeral value easily.

Quote:

Originally Posted by shifter

Now my problem is the following:

if (event->mask & IN_ISDIR) printf("IS A DIRECTORY");

but gcc outputs 'error: dereferencing pointer to incomplete type'.
Now what is the problem????
I am despaired...

In your code, is “event” a pointer to a struct inotify_event or is event itself a struct inotify_event? You can’t use pointer syntax with a struct (i.e., instead of “event->mask” try “event.mask”).

shifter · 04-02-2007, 08:20 PM

Problem resolved, ...
The syntax is correct, but I did not declare correctly event structure.

event_inotify* event instead inotify_event*

shifter · 06-21-2007, 06:14 PM

Exist it a method for tracing if I make subdirectory into directory monitored with inotify (like IN_CREATE, IN_ATTRIB...)

Thanks to help in advance.