kernel+libc: Add the write() system call, and fwrite()

kernel/src/sys/file.cpp

@@ -26,3 +26,26 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
 
     return nread;
 }
+
+Result<u64> sys_write(Registers*, SyscallArgs args)
+{
+    int fd = (int)args[0];
+    const u8* buf = (const u8*)args[1];
+    usize size = (usize)args[2];
+
+    if (!MemoryManager::validate_user_read(buf, size)) return err(EFAULT);
+
+    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
+
+    Thread* current = Scheduler::current();
+
+    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+
+    if (!descriptor.has_value()) return err(EBADF);
+
+    usize nwritten = TRY(descriptor->inode->write(buf, descriptor->offset, size));
+
+    descriptor->offset += nwritten;
+
+    return nwritten;
+}

libc/include/stdio.h

@@ -35,7 +35,8 @@ extern "C"
     /* Read arbitrarily sized items from a stream. */
     size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream);
 
-    size_t fwrite(const void*, size_t, size_t, FILE*);
+    /* Write arbitrarily sized items to a stream. */
+    size_t fwrite(const void* buf, size_t size, size_t nmemb, FILE* stream);
 
     int fseek(FILE*, long, int);
     long ftell(FILE*);

libc/include/unistd.h

@@ -38,6 +38,9 @@ extern "C"
     /* Read bytes from a file descriptor. */
     ssize_t read(int fd, void* buf, size_t size);
 
+    /* Write bytes to a file descriptor. */
+    ssize_t write(int fd, const void* buf, size_t size);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/stdio.cpp

@@ -66,6 +66,15 @@ extern "C"
             return (size_t)nread / size;
     }
 
+    size_t fwrite(const void* buf, size_t size, size_t nmemb, FILE* stream)
+    {
+        if (size * nmemb == 0) return 0;
+
+        ssize_t nwrite = write(stream->_fd, buf, size * nmemb);
+
+        return (size_t)nwrite / size;
+    }
+
     int ferror(FILE* stream)
     {
         return stream->_err;

libc/src/unistd.cpp

@@ -54,4 +54,10 @@ extern "C"
         long rc = syscall(SYS_read, fd, buf, size);
         __errno_return(rc, ssize_t);
     }
+
+    ssize_t write(int fd, const void* buf, size_t size)
+    {
+        long rc = syscall(SYS_write, fd, buf, size);
+        __errno_return(rc, ssize_t);
+    }
 }

libluna/include/luna/Syscall.h

@@ -2,7 +2,7 @@
 
 #define enumerate_syscalls(_e)                                                                                         \
     _e(exit) _e(console_write) _e(clock_gettime) _e(allocate_memory) _e(deallocate_memory) _e(usleep) _e(open)         \
-        _e(close) _e(read) _e(getpid)
+        _e(close) _e(read) _e(getpid) _e(write)
 
 enum Syscalls
 {