[zz] 浅析dev目录下设备文件mknod节点gid,uid和mode的如何方便设置

init

=
>
handle_device_fd 收到uevent信息

=
>
handle_device_event

=
>

static
void
handle_device_event(
struct
uevent *
uevent)

{

.
.
.

/* are we block or char? where should we live? */

if
(
!
strncmp
(
uevent-
>
path,
"/block"
,
6)
)
{

block =
1;

base =
"/dev/block/"
;
//根据uevent路径改变该节点路径

mkdir(
base,
0755)
;

}
else
{

block =
0;

/* this should probably be configurable somehow */

if
(
!
strncmp
(
uevent-
>
path,
"/class/graphics/"
,
16)
)
{

base =
"/dev/graphics/"
;
//

根据uevent路径

改变该uevent需要创建节点的路径

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/oncrpc/"
,
14)
)
{

base =
"/dev/oncrpc/"
;

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/adsp/"
,
12)
)
{

base =
"/dev/adsp/"
;

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/input/"
,
13)
)
{

base =
"/dev/input/"
;
//

根据uevent路径

改变该uevent需要创建节点的路径

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/sensors/"
,
15)
)
{

base =
"/dev/sensors/"
;

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/mtd/"
,
11)
)
{

base =
"/dev/mtd/"
;
//

根据uevent路径

改变该uevent需要创建节点的路径

mkdir(
base,
0755)
;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/misc/"
,
12)
&
&

!
strncmp
(
name,
"log_"
,
4)
)
{

base =
"/dev/log/"
;
//

根据uevent路径

改变该uevent需要创建节点的路径

mkdir(
base,
0755)
;

name +
=
4;

}
else
if
(
!
strncmp
(
uevent-
>
path,
"/class/sound/"
,
13)
)
{

base =
"/dev/snd/"
;

mkdir(
base,
0755)
;

}
else

base =
"/dev/"
;

}

snprintf(
devpath,
sizeof
(
devpath)
,
"%s%s"
,
base,
name)
;

if
(
!
strcmp
(
uevent-
>
action,
"add"
)
)
{

make_device(
devpath,
block,
uevent-
>
major,
uevent-
>
minor)
;
//创建节点文件文件devpath

return
;

}

.
.
.

}

static
void
make_device(
const
char
*
path,
int
block,
int
major,
int
minor)

{

unsigned
uid;

unsigned
gid;

mode_t mode;

dev_t dev;

if
(
major >
255 |
|
minor >
255)

return
;

mode =
get_device_perm(
path,
&
uid,
&
gid)
|
(
block ?
S_IFBLK :
S_IFCHR)
;
//获取将要创建的节点是否需要重设它的mode数值

dev =
(
major <
<
8)
|
minor;

mknod(
path,
mode,
dev)
;

chown(
path,
uid,
gid)
;

}

get_device_perm函数会比较path路径是否和下面的devperms[
]
数组中的inode路径相一致,
如果一致,
那么返回devperms[
]
数组中指定的uid,
gid和mode数值,
这样make_device就会向/
dev这个tmpfs'内存虚拟物理盘'
创建inode节点,
同时改变该inode的uid和gid.

于是在devperms[
]
数组中我们就可以方便的控制生成的/
dev文件的uid,
gid和mode了.

static
struct
perms_ devperms[
]
=
{

{
"/dev/null"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/zero"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/full"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/ptmx"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/tty"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/random"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/urandom"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/ashmem"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/binder"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/m2d"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/bmm"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/innodev"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/innodev0"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/innodev1"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

{
"/dev/innodev2"
,
0666,
AID_ROOT,
AID_ROOT,
0 }
,

/* logger should be world writable (for logging) but not readable */

{
"/dev/log/"
,
0662,
AID_ROOT,
AID_LOG,
1 }
,

/* these should not be world writable */

{
"/dev/android_adb"
,
0660,
AID_ADB,
AID_ADB,
0 }
,

{
"/dev/android_adb_enable"
,
0660,
AID_ADB,
AID_ADB,
0 }
,

{
"/dev/ttyMSM0"
,
0660,
AID_BLUETOOTH,
AID_BLUETOOTH,
0 }
,

{
"/dev/alarm"
,
0664,
AID_SYSTEM,
AID_RADIO,
0 }
,

{
"/dev/tty0"
,
0666,
AID_ROOT,
AID_SYSTEM,
0 }
,

{
"/dev/graphics/"
,
0666,
AID_ROOT,
AID_GRAPHICS,
1 }
,

{
"/dev/hw3d"
,
0660,
AID_SYSTEM,
AID_GRAPHICS,
0 }
,

{
"/dev/input/"
,
0660,
AID_ROOT,
AID_INPUT,
1 }
,

{
"/dev/eac"
,
0660,
AID_ROOT,
AID_AUDIO,
0 }
,

{
"/dev/cam"
,
0660,
AID_ROOT,
AID_CAMERA,
0 }
,

{
"/dev/video0"
,
0660,
AID_ROOT,
AID_CAMERA,
0 }
,

{
"/dev/mved"
,
0660,
AID_SYSTEM,
AID_CAMERA,
0 }
,

{
"/dev/pmem"
,
0660,
AID_SYSTEM,
AID_GRAPHICS,
0 }
,

{
"/dev/pmem_gpu"
,
0660,
AID_SYSTEM,
AID_GRAPHICS,
1 }
,

{
"/dev/pmem_adsp"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/pmem_camera"
,
0660,
AID_SYSTEM,
AID_CAMERA,
1 }
,

{
"/dev/oncrpc/"
,
0660,
AID_ROOT,
AID_SYSTEM,
1 }
,

{
"/dev/adsp/"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/sensors/"
,
0666,
AID_SYSTEM,
AID_SYSTEM,
1 }
,

{
"/dev/mt9t013"
,
0660,
AID_SYSTEM,
AID_SYSTEM,
0 }
,

{
"/dev/akm8976_daemon"
,
0640,
AID_COMPASS,
AID_SYSTEM,
0 }
,

{
"/dev/akm8976_aot"
,
0640,
AID_COMPASS,
AID_SYSTEM,
0 }
,

{
"/dev/akm8976_pffd"
,
0640,
AID_COMPASS,
AID_SYSTEM,
0 }
,

{
"/dev/msm_pcm_out"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/msm_pcm_in"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/msm_pcm_ctl"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/msm_mp3"
,
0660,
AID_SYSTEM,
AID_AUDIO,
1 }
,

{
"/dev/smd0"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/qmi"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/qmi0"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/qmi1"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/qmi2"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/htc-acoustic"
,
0640,
AID_RADIO,
AID_RADIO,
0 }
,

{
"/dev/snd/"
,
0666,
AID_ROOT,
AID_AUDIO,
1 }
,

{
NULL
,
0,
0,
0,
0 }
,

}
;