From 08f4db4d2b29f8132fd05e8d38122cc81b1f6d82 Mon Sep 17 00:00:00 2001
From: root <>
Date: Wed, 7 May 2025 10:29:21 +0000
Subject: [PATCH] poll(2) on the server socket; pollfds array

---
 constants.c |  3 ++
 hello.s     | 79 +++++++++++++++++++++++++++++++++++++++++++++++++----
 makefile    |  2 +-
 3 files changed, 77 insertions(+), 7 deletions(-)

diff --git a/constants.c b/constants.c
index 9f9db6e..cc8ec0b 100644
--- a/constants.c
+++ b/constants.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <sys/socket.h>
 #include <fcntl.h>
+#include <poll.h>
 
 //    printf("x %d\n", x);
 void main() {
@@ -11,4 +12,6 @@ void main() {
     printf("O_NONBLOCK      %d\n", O_NONBLOCK);
     printf("sizeof(int)     %d\n", sizeof(int));
     printf("sizeof(short)   %d\n", sizeof(short));
+    printf("POLLIN          %d\n", POLLIN);
+    printf("POLLOUT         %d\n", POLLOUT);
 }
diff --git a/hello.s b/hello.s
index 6ab1bde..091ea49 100644
--- a/hello.s
+++ b/hello.s
@@ -3,6 +3,7 @@ global _start
 ; constants
 SYS_READ        equ 0
 SYS_WRITE       equ 1
+SYS_POLL        equ 7
 SYS_SENDFILE    equ 40
 SYS_SOCKET      equ 41
 SYS_ACCEPT      equ 43
@@ -17,16 +18,22 @@ SOCK_STREAM     equ 1
 F_GETFL         equ 3
 F_SETFL         equ 4
 O_NONBLOCK      equ 2048
+POLLIN          equ 1
+POLLOUT         equ 4
+
+pollfd_size equ 4 + 2 + 2  ; $ man 2 poll
+pollfds_capacity equ 100
 
 SECTION .data
 hello           db "Hello world!", 0x0a
 hello_len       equ $ - hello
 server_path     db "server.sock", 0x00
 server_path_len equ $ - hello
-sockaddr_len    equ 110 ; $ man 7 unix
+sockaddr_size   equ 2 + 108  ; $ man 7 unix
 
 SECTION .bss
-sockaddr    resb sockaddr_len
+sockaddr    resb sockaddr_size
+pollfds     resb pollfd_size * pollfds_capacity
 
 SECTION .text
 
@@ -38,9 +45,20 @@ _start:
     syscall
 
     call make_server
-    push rax
-    call accept
-    pop r10
+    mov rbx, 0  ; pollfd array length
+    mov ebp, eax  ; server fd
+
+    mov rax, rbx
+    mov edi, ebp
+    mov si, POLLIN
+    call pollfds__append
+    mov rbx, rax
+
+    mov rax, SYS_POLL
+    mov rdi, pollfds
+    mov rsi, rbx
+    mov rdx, 5000
+    syscall
 
 exit:
     mov rax, SYS_EXIT
@@ -55,6 +73,55 @@ accept:
     syscall
     ret
 
+; rax - array length
+; edi - fd
+; si - events
+; Returns new array length in rax
+pollfds__append:
+    mov [pollfds + rax], edi
+    mov [pollfds + rax + 4], si
+    add rax, 1
+    ret
+
+; Returns new array length in rax
+; rax - array length
+; edi - fd
+pollfds__remove:
+    mov r10d, edi
+    mov rdi, 0
+
+; Variables:
+; rax - array length
+; rdi - array index
+; r10d - fd
+; r11d - pollfds[rdi].fd
+pollfds__remove__loop:
+    cmp rdi, rax
+    jge return  ; fd was not found
+    mov r11d, [pollfds + rdi * pollfd_size]
+    add rdi, 1
+    cmp r11d, r10d
+    jne pollfds__remove__loop
+    sub rdi, 1
+
+; Returns new array length in rax
+; rax - array length
+; rdi - array index to remove
+pollfds__remove_index:
+    cmp rax, 1
+    jle pollfds__clear
+    mov r10d, [pollfds + (rax - 1) * pollfd_size]
+    mov [pollfds + rdi * pollfd_size], r10d
+    sub rax, 1
+    ret
+
+; Returns new array length in rax
+; rax - array length
+pollfds__clear:
+    mov rax, 0
+    ret
+
+; Returns (in rax) the server's file descriptor
 make_server:
     mov rax, SYS_UNLINK
     mov rdi, server_path
@@ -74,7 +141,7 @@ make_server:
     mov rax, SYS_BIND
     mov rdi, r10
     mov rsi, sockaddr
-    mov rdx, sockaddr_len
+    mov rdx, sockaddr_size
     syscall
 
     mov rax, SYS_LISTEN
diff --git a/makefile b/makefile
index 4ec5593..d03c95d 100644
--- a/makefile
+++ b/makefile
@@ -1,3 +1,3 @@
 main:
-	nasm -f elf64 -o hello.o hello.s
+	nasm -g -f elf64 -o hello.o hello.s
 	ld -o hello hello.o