Linux Drivers Concept

[zdbrig]

Hello,

I am software developer, and I am new in kernel programming.
I have token a look at linux sources, I found that drivers of all hardware are included in linux kernel sources. The question is, how Linux include this drivers on the Kernel ??

- Including drivers statically in the the kernel is illogical of course. Since drivers will be loaded, all of them, even if they are not used.
- making drivers as dynamic libraries (.so) is not sufficient, too. How does the kernel include this library if it was already compiled and build ?

Moreover, will Linux sources grow every time a new driver take place ? this causes many troubles:
- Compiling linux will become slower year after year.
- linux evolution will be difficult because next versions must support old drivers.
- Linux Distributions will be huge in size.

Is Linux planning for solutions to that problems ?

[bigtomrodney]

Linux loads kernel modules containing drivers. If hardware is detected the correct module is loaded. I believe the extension if used is .ko (kernel object?)

The drivers are pretty small and when you compile Linux you only compile what you want to. If you look at menuconfig you can see that everything is optional.

[zdbrig]

So can we add a new driver to an existing Linux system, without recompiling the kernel ?

[bigtomrodney]

Yep you can just compile that module and then load it using insmod/modprobe. The nVidia and AMD drivers do just that, the compile their kernel interface module and load it. You don't need to reboot or anything.

[HROAdmin26]

Basic drivers that are *typically* needed by any system are usually compiled statically into the kernel. Everything else is commonly compiled as modules.

Google: linux driver coding module

You see lots of device drivers when you lsmod (list modules):

lsmod
Module                  Size  Used by
nls_utf8               18432  2 
cifs                  228592  2 
nfs                   239660  2 
lockd                  76408  2 nfs
nfs_acl                19840  1 nfs
sunrpc                173308  4 nfs,lockd,nfs_acl
sha256                 27520  0 
aes_i586               49524  2 
cbc                    20736  1 
blkcipher              22404  1 cbc
dm_crypt               29192  1 
vmnet                  67472  15 
vmmon                 121840  6 
snd_pcm_oss            62720  0 
snd_mixer_oss          32384  1 snd_pcm_oss
snd_seq                66740  0 
snd_seq_device         24460  1 snd_seq
iptable_filter         19200  0 
ip_tables              28996  1 iptable_filter
ip6_tables             30148  0 
x_tables               30596  2 ip_tables,ip6_tables
microcode              30092  0 
firmware_class         25856  1 microcode
cpufreq_conservative    23560  0 
cpufreq_userspace      22912  0 
cpufreq_powersave      18176  0 
acpi_cpufreq           26888  0 
speedstep_lib          21508  0 
apparmor               53024  0 
ext2                   76296  1 
mbcache                24580  1 ext2
xfs                   515220  1 
loop                   33924  0 
dm_mod                 69168  3 dm_crypt
snd_hda_intel         285212  3 
snd_pcm                94852  3 snd_pcm_oss,snd_hda_intel
snd_timer              39044  3 snd_seq,snd_pcm
snd                    70452  11 snd_pcm_oss,snd_mixer_oss,snd_seq,snd_seq_device,snd_hda_intel,snd_pcm,snd_timer
soundcore              23748  1 snd
e1000                 180288  0 
fglrx                1686092  27 
snd_page_alloc         26248  2 snd_hda_intel,snd_pcm
i2c_i801               24848  0 
rtc_cmos               24352  0 
i2c_core               39808  1 i2c_i801
intel_agp              39572  0 
parport_pc             53436  0 
rtc_core               35336  1 rtc_cmos
button                 24720  0 
parport                50120  1 parport_pc
sr_mod                 31780  0 
agpgart                48180  2 fglrx,intel_agp
rtc_lib                19328  1 rtc_core
generic                21124  0 [permanent]
serio_raw              23044  0 
e1000e                105124  0 
joydev                 25920  0 
ide_core              135492  1 generic
cdrom                  49308  1 sr_mod
sg                     49196  0 
usbhid                 53716  0 
hid                    41472  1 usbhid
ff_memless             21640  1 usbhid
raid456               136720  0 
xor                    30856  1 raid456
raid1                  38656  1 
sd_mod                 43392  11 
ehci_hcd               47500  0 
uhci_hcd               39440  0 
usbcore               136044  4 usbhid,ehci_hcd,uhci_hcd
edd                    25284  0 
raid0                  24320  3 
reiserfs              245556  2 
fan                    21508  0 
ahci                   41476  9 
ata_generic            23812  0 
libata                149320  2 ahci,ata_generic
scsi_mod              152664  4 sr_mod,sg,sd_mod,libata
thermal                32136  0 
processor              54312  2 acpi_cpufreq,thermal

[zdbrig]

Thank you for help.
That's the first time I read about Kernel Objects.
I found this book very useful for understanding kernel module programming: Linux Device Drivers, 2nd Edition: Online Book
Did you know why hardware drivers are rarely done by manufacturers and usually by third parties ?