Solved Issue with ioctl(2) request to ACPI battery.

A

artembunichev

Hi everybody!

I'm writing a simple C program that can read battery information. I'm sending a ACPIIO_BATT_GET_BATTINFO ioctl(2) request to /dev/acpi device. And it seems to work.

However, ioctl(2) request exits with error "Device not configured" when I put inside the loop. Here's the program sample:

C: 
#include<fcntl.h>
#include<stdint.h>
#include<dev/acpica/acpiio.h>
#include<sys/ioctl.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>

int main() {
    int acpifd;
    union acpi_battery_ioctl_arg batio;
    struct acpi_battinfo* batinf;
  
    acpifd = open("/dev/acpi", O_RDONLY);
    if (acpifd == -1) {
        dprintf(2, "can't open /dev/acpi file.\n");
        return 1;
    }
  
    int i = 0;
    while(i < 2) {
        if (ioctl(acpifd, ACPIIO_BATT_GET_BATTINFO, &batio) == -1) {
            dprintf(2, "can't send an ioctl(2) request to /dev/acpi.\n");
            dprintf(2, "err: %s\n", strerror(errno));
            return 1;
        }
      
        dprintf(1, "no error.\n");
        ++i;
    }
  
    return 0;
}

When I do like this:

Code: 
diff --git a/acpi1.c b/acpi2.c
index 0ebce72..e659bc4 100644
--- a/acpi1.c
+++ b/acpi2.c
@@ -18,7 +18,7 @@ int main() {
     }
  
     int i = 0;
-    while(i < 2) {
+    //while(i < 2) {
         if (ioctl(acpifd, ACPIIO_BATT_GET_BATTINFO, &batio) == -1) {
             dprintf(2, "can't send an ioctl(2) request to /dev/acpi.\n");
             dprintf(2, "err: %s\n", strerror(errno));
@@ -27,7 +27,7 @@ int main() {
      
         dprintf(1, "no error.\n");
         ++i;
-    }
+    //}
  
     return 0;
 }

i.e. remove the loop, the request is successful.

What may be the actual cause of that? Am I missing something? I consulted the acpi_battery(4) manual, but I didn't find anything that would be related to this problem. Also I looked into the actual source code - I found that this particular acpi(2) request fails with this error code in this case (the code is taken from /usr/src/sys/dev/acpica/acpi_battery.c, function acpi_battery_get_battinfo):

C: 
/*
     * Get the battery devclass and max unit for battery devices.  If there
     * are none or error, return immediately.
     */
    batt_dc = devclass_find("battery");
    if (batt_dc == NULL)
    return (ENXIO);
    devcount = devclass_get_maxunit(batt_dc);
    if (devcount == 0)
    return (ENXIO);

Even though I found that, it, unfortunately, doesn't make the things clear for me - I still can't understand what's the cause of the problem and how to fix it.

Would you please help me?


Artem.
 
eseipi said:
The problem is not the loop, but the fact that you did not initialize batio.unit. For an example of usage, see /usr/src/usr.sbin/acpi/acpiconf/acpiconf.c.
Click to expand...
Oh, now I can see, thank you very much, eseipi!

By the way, seems that it's also written in acpi_battery(4) man page, but in not that obvious form:
Code: 
IOCTLS
       Every ioctl for the acpi_battery    driver takes a    single    integer     value
       for  the     battery  unit    number    as an argument,    and returns a specific
       structure    for       each       request.    A    special    unit    number
       ACPI_BATTERY_ALL_UNITS  specifies all of    the attached units and reports
       accumulated information.

I havn't been working with ioctl's that much, so I want to ask did I get it right that in case of this ACPI request, we use the same structure acpi_battery_ioctl_arg for both input arguments (in this case it's unit member) and request response ( battinfo and others)?
 
artembunichev said:
I havn't been working with ioctl's that much, so I want to ask did I get it right that in case of this ACPI request, we use the same structure acpi_battery_ioctl_arg for both input arguments (in this case it's unit member) and request response ( battinfo and others)?
Click to expand...
Yes, that's right. Just a small note: acpi_battery_ioctl_arg is a union, not a structure.
 
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