As opposed to FreeBSD, the cdevsw structs are built out by a macro, this macro will take the number of devices being initialized, and the name of the module passed to it (e.g. "cdev_example_init(1, example)") and fill out struct cdevsw to point to the appropriate functions via name concatenation (e.g. the open function will be registered as exampleopen).
I begin by adding a cdev_example_init macro to sys/sys/conf.h, then call the macro within the cdevsw[] array in sys/arch/amd64/amd64/conf.c. Also, while I'm in here, I add a call to the cdev_decl() macro. This should take care of the cdevsw setup portion of the code.
From there, I add example.c under sys/dev/ and build out basic open, close, read, and write functions for it, and add it to files.conf. Much to my surprise, after fixing a few compile errors for missing headers, the kernel compiles and installs fine. Once the machine had booted into my new kernel, I ran a "doas mknod /dev/example c 98 0" to create a node for the device in /dev. In this case, 98 was the position in the cdevsw[] array where my call to cdev_exampl_init landed. In OpenBSD, the major node number is simply an index into the cdevsw array.
I had to switch from using copystr to uiomove in order to get I/O working properly, but once I did, the basic interface code worked fine.
Finally, I decided to work with the MAKEDEV script to ensure that my device would be present in a release, if I so chose to make one. The script required me to add a new case for "example)" with a call to the M function and a few parameters to set the device node name, Major/Minor numbers, permissions, and ownership. In order for etc/etc.amd64/MAKEDEV to be copied to /dev by sysmerge, I had to do a full build of the system. This is a bit time consuming, and there might be a better way, but it worked for my immediate purposes.
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| Index: etc/etc.amd64/MAKEDEV | |
| =================================================================== | |
| RCS file: /cvs/src/etc/etc.amd64/MAKEDEV,v | |
| retrieving revision 1.118 | |
| diff -u -p -u -p -r1.118 MAKEDEV | |
| --- etc/etc.amd64/MAKEDEV 14 Nov 2017 20:22:04 -0000 1.118 | |
| +++ etc/etc.amd64/MAKEDEV 5 Mar 2018 19:32:55 -0000 | |
| @@ -251,6 +251,10 @@ switch*) | |
| M switch$U c 97 $U 600 | |
| ;; | |
| +example) | |
| + M example c 98 0 660 | |
| + ;; | |
| + | |
| pvbus*) | |
| M pvbus$U c 95 $U 640 | |
| ;; | |
| @@ -575,7 +579,7 @@ all) | |
| R lpa2 lpt0 lpt1 lpt2 tty00 tty01 tty02 tty03 tty04 tty05 | |
| R tty06 tty07 tty08 tty09 tty0a tty0b ttyc0 ttyc1 ttyc2 ttyc3 | |
| R ttyc4 ttyc5 ttyc6 ttyc7 apm pf pctr wd0 wd1 wd2 wd3 std st0 | |
| - R st1 fd | |
| + R st1 fd example | |
| ;; | |
| wd*|sd*) | |
| Index: sys/arch/amd64/amd64/conf.c | |
| =================================================================== | |
| RCS file: /cvs/src/sys/arch/amd64/amd64/conf.c,v | |
| retrieving revision 1.60 | |
| diff -u -p -u -p -r1.60 conf.c | |
| --- sys/arch/amd64/amd64/conf.c 4 Sep 2016 10:51:23 -0000 1.60 | |
| +++ sys/arch/amd64/amd64/conf.c 5 Mar 2018 19:33:14 -0000 | |
| @@ -116,6 +116,7 @@ int nblkdev = nitems(bdevsw); | |
| #define mmread mmrw | |
| #define mmwrite mmrw | |
| cdev_decl(mm); | |
| +cdev_decl(example); | |
| cdev_decl(wd); | |
| #include "bio.h" | |
| #include "pty.h" | |
| @@ -297,6 +298,7 @@ struct cdevsw cdevsw[] = | |
| cdev_pvbus_init(NPVBUS,pvbus), /* 95: pvbus(4) control interface */ | |
| cdev_ipmi_init(NIPMI,ipmi), /* 96: ipmi */ | |
| cdev_switch_init(NSWITCH,switch), /* 97: switch(4) control interface */ | |
| + cdev_example_init(1,example) /* 98: example character device */ | |
| }; | |
| int nchrdev = nitems(cdevsw); | |
| Index: sys/conf/files | |
| =================================================================== | |
| RCS file: /cvs/src/sys/conf/files,v | |
| retrieving revision 1.660 | |
| diff -u -p -u -p -r1.660 files | |
| --- sys/conf/files 14 Feb 2018 23:51:49 -0000 1.660 | |
| +++ sys/conf/files 5 Mar 2018 19:33:14 -0000 | |
| @@ -430,6 +430,9 @@ file dev/ic/malo.c malo | |
| device bwi: ether, ifnet, ifmedia, firmload, wlan | |
| file dev/ic/bwi.c bwi | |
| +# PHE Example Device | |
| +file dev/example.c | |
| + | |
| # Attributes which machine-independent bus support can be attached to. | |
| # These should be defined here, because some of these busses can have | |
| # devices which provide these attributes, and we'd like to avoid hairy | |
| Index: sys/dev/example.c | |
| =================================================================== | |
| RCS file: sys/dev/example.c | |
| diff -N sys/dev/example.c | |
| --- /dev/null 1 Jan 1970 00:00:00 -0000 | |
| +++ sys/dev/example.c 5 Mar 2018 19:33:14 -0000 | |
| @@ -0,0 +1,34 @@ | |
| +#include <sys/types.h> | |
| +#include <sys/time.h> | |
| +#include <sys/uio.h> | |
| +#include <sys/vnode.h> | |
| +#include <sys/systm.h> | |
| + | |
| +static char buf[512 + 1]; | |
| + | |
| +int | |
| +exampleopen(dev_t dev, int flag, int mode, struct proc *p) | |
| +{ | |
| + memset(&buf, '\0', 513); | |
| + return 0; | |
| +} | |
| + | |
| +int | |
| +exampleclose(dev_t dev, int flag, int mode, struct proc *p) | |
| +{ | |
| + return 0; | |
| +} | |
| + | |
| +int | |
| +exampleread(dev_t dev, struct uio *uio, int flags) | |
| +{ | |
| + uiomove(&buf, 513, uio); | |
| + return 0; | |
| +} | |
| + | |
| +int | |
| +examplewrite(dev_t dev, struct uio *uio, int flags) | |
| +{ | |
| + uiomove(&buf, 513, uio); | |
| + return 0; | |
| +} | |
| Index: sys/sys/conf.h | |
| =================================================================== | |
| RCS file: /cvs/src/sys/sys/conf.h,v | |
| retrieving revision 1.144 | |
| diff -u -p -u -p -r1.144 conf.h | |
| --- sys/sys/conf.h 13 Jan 2018 13:03:42 -0000 1.144 | |
| +++ sys/sys/conf.h 5 Mar 2018 19:33:15 -0000 | |
| @@ -475,6 +475,12 @@ extern struct cdevsw cdevsw[]; | |
| (dev_type_stop((*))) enodev, 0, (dev_type_poll((*))) enodev, \ | |
| (dev_type_mmap((*))) enodev, 0 } | |
| +/* open, close, read, write */ | |
| +#define cdev_example_init(c,n) { \ | |
| + dev_init(c,n,open), dev_init(c,n,close), dev_init(c,n,read), \ | |
| + dev_init(c,n,write), (dev_type_ioctl((*))) enodev, \ | |
| + (dev_type_stop((*))) enodev, 0, seltrue, (dev_type_mmap((*))) enodev } | |
| + | |
| #endif | |
| /* |
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| #include <fcntl.h> | |
| #include <stdio.h> | |
| #include <string.h> | |
| #include <unistd.h> | |
| #include <errno.h> | |
| #include <stdlib.h> | |
| int main(int argc, char *argv[]) { | |
| int kernel_fd; | |
| size_t len; | |
| static char buf[512 + 1]; | |
| errno = 0; | |
| kernel_fd = open(argv[1], O_RDWR); | |
| if (kernel_fd == -1) { | |
| perror("open"); | |
| exit(EXIT_FAILURE); | |
| } | |
| len = strlen(argv[2]); | |
| write(kernel_fd, argv[2], len + 1); | |
| printf("Wrote \"%s\" to %s\n", argv[2], argv[1]); | |
| read(kernel_fd, buf, len + 1); | |
| printf("Read \"%s\" from %s\n", buf, argv[1]); | |
| return 0; | |
| } |
