Kernel/LibC: Implement pread()

kernel/include/kernel/Process.h

@@ -105,6 +105,8 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_readlink(const char* path, char* buffer, size_t bufsize);
 		BAN::ErrorOr<long> sys_readlinkat(int fd, const char* path, char* buffer, size_t bufsize);
 
+		BAN::ErrorOr<long> sys_pread(int fd, void* buffer, size_t count, off_t offset);
+
 		BAN::ErrorOr<long> sys_chmod(const char*, mode_t);
 
 		BAN::ErrorOr<long> sys_pipe(int fildes[2]);

kernel/kernel/Process.cpp

@@ -823,6 +823,14 @@ namespace Kernel
 		return readlink_impl(absolute_path.sv(), buffer, bufsize);
 	}
 
+	BAN::ErrorOr<long> Process::sys_pread(int fd, void* buffer, size_t count, off_t offset)
+	{
+		LockGuard _(m_lock);
+		validate_pointer_access(buffer, count);
+		auto inode = TRY(m_open_file_descriptors.inode_of(fd));
+		return TRY(inode->read(offset, { (uint8_t*)buffer, count }));
+	}
+
 	BAN::ErrorOr<long> Process::sys_chmod(const char* path, mode_t mode)
 	{
 		if (mode & S_IFMASK)

kernel/kernel/Syscall.cpp

@@ -220,6 +220,9 @@ namespace Kernel
 		case SYS_MSYNC:
 			ret = Process::current().sys_msync((void*)arg1, (size_t)arg2, (int)arg3);
 			break;
+		case SYS_PREAD:
+			ret = Process::current().sys_pread((int)arg1, (void*)arg2, (size_t)arg3, (off_t)arg4);
+			break;
 		default:
 			dwarnln("Unknown syscall {}", syscall);
 			break;

libc/include/sys/syscall.h

@@ -62,6 +62,7 @@ __BEGIN_DECLS
 #define SYS_READLINK 59
 #define SYS_READLINKAT 60
 #define SYS_MSYNC 61
+#define SYS_PREAD 62
 
 __END_DECLS
 

libc/unistd.cpp

@@ -88,6 +88,11 @@ ssize_t readlinkat(int fd, const char* __restrict path, char* __restrict buf, si
 	return syscall(SYS_READLINKAT, fd, path, buf, bufsize);
 }
 
+ssize_t pread(int fildes, void* buf, size_t nbyte, off_t offset)
+{
+	return syscall(SYS_PREAD, fildes, buf, nbyte, offset);
+}
+
 int dup(int fildes)
 {
 	return syscall(SYS_DUP, fildes);