Bugfix (#1190)

* posix_file_lock: pass lockp directly to fcntl\n\nBugfix: previously passed address-of pointer variable, causing fcntl to receive an invalid pointer (EFAULT/lock failure). Aligns with POSIX fcntl(fd, cmd, struct flock*). Pure fix.

* mfc: fix scatter write loop to use current element (i->base/len)\n\nBugfix: loop used scats->base/len, repeating the first buffer each iteration. Use iterator element to write each scatter segment.

* posix_file: copy-assign uses dup when target fd==-1 (unlikely), else dup2\n\nIf target is closed, duplicate source fd; otherwise reuse target via dup2. Avoids dup2(old,-1) failure; no source-closed special-casing.

Author: mq-loser

include/fast_io_driver/mfc_impl/mfc_file.h

@@ -99,7 +99,7 @@ inline void mfc_scatter_write_impl(CFile *cfp, io_scatter_t const *scats, ::std:
 	auto e{scats + n};
 	for (; i != e; ++i)
 	{
-		mfc_write_n_impl(cfp, reinterpret_cast<::std::byte const *>(scats->base), scats->len);
+		mfc_write_n_impl(cfp, reinterpret_cast<::std::byte const *>(i->base), i->len);
 	}
 }
 

include/fast_io_hosted/platforms/posix.h

@@ -1273,7 +1273,14 @@ class basic_posix_family_file : public basic_posix_family_io_observer<family, ch
 		{
 			return *this;
 		}
-		this->fd = ::fast_io::details::sys_dup2(dp.fd, this->fd);
+		if (this->fd == -1) [[unlikely]]
+		{
+			this->fd = ::fast_io::details::sys_dup(dp.fd);
+		}
+		else
+		{
+			this->fd = ::fast_io::details::sys_dup2(dp.fd, this->fd);
+		}
 		return *this;
 	}
 	inline constexpr basic_posix_family_file(basic_posix_family_file &&__restrict b) noexcept

include/fast_io_hosted/platforms/posix_file_lock.h

@@ -6,7 +6,7 @@ namespace details
 {
 inline int fcntl_file_lock(int fd, int cmd, struct flock const *lockp)
 {
-	return ::fcntl(fd, cmd, __builtin_addressof(lockp));
+	return ::fcntl(fd, cmd, lockp);
 }
 
 inline void posix_file_lock_lock_common_impl(int fd, struct flock const &lockp)