kboot: Implement mkdir(2)

mkdir() may be needed early in boot to create missing
directories. Provide a syscall wrapper for it.

Sponsored by:		Netflix

stand/kboot/arch/amd64/syscall_nr.h

@@ -5,6 +5,7 @@
 #define SYS_gettimeofday	 96
 #define SYS_kexec_load		246
 #define SYS_lseek		  8
+#define	SYS_mkdirat		258
 #define SYS_mmap		  9
 #define	SYS_munmap		 11
 #define SYS_newfstat		  5

stand/kboot/arch/powerpc64/syscall_nr.h

@@ -6,6 +6,7 @@
 #define SYS_gettimeofday	 78
 #define SYS_kexec_load		268
 #define SYS_llseek		140
+#define	SYS_mkdirat		287
 #define SYS_mmap		 90
 #define	SYS_munmap		 91
 #define SYS_newfstat		SYS_fstat

stand/kboot/host_syscall.h

@@ -99,6 +99,7 @@ int host_getpid(void);
 int host_gettimeofday(struct host_timeval *a, void *b);
 int host_kexec_load(uint32_t start, int nsegs, uint32_t segs, uint32_t flags);
 ssize_t host_llseek(int fd, int32_t offset_high, int32_t offset_lo, uint64_t *result, int whence);
+int host_mkdir(const char *, host_mode_t);
 void *host_mmap(void *addr, size_t len, int prot, int flags, int fd, off_t off);
 int host_munmap(void *addr, size_t len);
 int host_open(const char *path, int flags, int mode);

stand/kboot/host_syscalls.c

@@ -63,6 +63,12 @@ host_llseek(int fd, int32_t offset_high, int32_t offset_lo, uint64_t *result, in
 #endif
 }
 
+int
+host_mkdir(const char *path, host_mode_t mode)
+{
+	return host_syscall(SYS_mkdirat, HOST_AT_FDCWD, (uintptr_t)path, mode);
+}
+
 void *
 host_mmap(void *addr, size_t len, int prot, int flags, int fd, off_t off)
 {