select() syscall for character device reads

include/sys/amd64/sys_file.h

@@ -2,6 +2,9 @@
 #include "sys/types.h"
 #include "sys/fs/dirent.h"
 #include "sys/stat.h"
+#include "sys/select.h"
+
+struct timeval;
 
 ssize_t sys_read(int fd, void *buf, size_t lim);
 ssize_t sys_write(int fd, const void *buf, size_t lim);
@@ -20,6 +23,11 @@ int sys_rmdir(const char *pathname);
 int sys_stat(const char *filename, struct stat *st);
 int sys_access(const char *path, int mode);
 
+// XXX: Except timeout is const, as I don't want to modify it
+//      No one cares about how much time is remaining once
+//      select() returns, right?
+int sys_select(int nfds, fd_set *rd, fd_set *wr, fd_set *exc, struct timeval *timeout);
+
 // TODO: const struct termios *termp, const struct winsize *winp
 int sys_openpty(int *master, int *slave);
 

include/sys/chr.h

@@ -1,8 +1,10 @@
 #pragma once
 #include "sys/types.h"
+#include "sys/ring.h"
 
 struct chrdev {
     void *dev_data;
+    struct ring buffer;
 
     ssize_t (*write) (struct chrdev *chr, const void *buf, size_t pos, size_t lim);
     ssize_t (*read) (struct chrdev *chr, void *buf, size_t pos, size_t lim);

include/sys/select.h

@@ -0,0 +1,30 @@
+#pragma once
+
+struct timeval;
+
+// 64 bits
+typedef long int __fd_mask;
+
+#define __NFDBITS       (8 * (int) sizeof(__fd_mask))
+// TODO: Guess this should be the same as the maximum
+//       per-process filedes count
+#define __FD_SETSIZE    64
+
+typedef struct {
+    __fd_mask fds_bits[__FD_SETSIZE / __NFDBITS];
+} fd_set;
+
+#define FD_SET(fd, fds)     \
+    (fds)->fds_bits[(fd) / __NFDBITS] |= (1ULL << ((fd) % __NFDBITS))
+
+#define FD_ISSET(fd, fds)   \
+    (!!((fds)->fds_bits[(fd) / __NFDBITS] & (1ULL << ((fd) % __NFDBITS))))
+
+#define FD_ZERO(fds)        \
+    for (int __i = 0; __i < (__FD_SETSIZE / __NFDBITS); ++__i) \
+        (fds)->fds_bits[__i] = 0
+
+#if !defined(__KERNEL__)
+// Implemented by libc
+int select(int nfds, fd_set *rd, fd_set *wr, fd_set *exc, struct timeval *tv);
+#endif

include/sys/syscall.h

@@ -7,6 +7,7 @@
 #define SYSCALL_NR_STAT         4
 #define SYSCALL_NR_LSEEK        8
 #define SYSCALL_NR_ACCESS       21
+#define SYSCALL_NR_SELECT       23
 #define SYSCALL_NR_GETCWD       79
 #define SYSCALL_NR_CHDIR        80
 #define SYSCALL_NR_MKDIR        83