libc: do not zero errno on success in vfs plugin

The manpage to errno tells the following story:

The <errno.h> header file defines the integer variable errno, which is
set by system calls and some library functions in the event of an error
to indicate what went wrong. Its value is significant only when the
return value of the call indicated an error (i.e., -1 from most system
calls; -1 or NULL from most library functions); a function that
succeeds is allowed to change errno.

Valid error numbers are all nonzero; errno is never set to zero by any
system call or library function.

repos/libports/src/lib/libc/vfs_plugin.cc

@@ -391,7 +391,6 @@ Libc::File_descriptor *Libc::Vfs_plugin::open(char const *path, int flags,
 		switch (_root_dir.open(path, flags, &handle)) {
 
 		case Result::OPEN_OK:
-			errno = 0;
 			break;
 
 		case Result::OPEN_ERR_UNACCESSIBLE:
@@ -405,7 +404,6 @@ Libc::File_descriptor *Libc::Vfs_plugin::open(char const *path, int flags,
 				switch (_root_dir.open(path, flags | O_EXCL, &handle)) {
 
 				case Result::OPEN_OK:
-					errno = 0;
 					break;
 
 				case Result::OPEN_ERR_EXISTS:
@@ -479,7 +477,7 @@ int Libc::Vfs_plugin::mkdir(const char *path, mode_t mode)
 	case Result::MKDIR_ERR_NO_SPACE:      errno = ENOSPC;       return -1;
 	case Result::MKDIR_ERR_NAME_TOO_LONG: errno = ENAMETOOLONG; return -1;
 	case Result::MKDIR_ERR_NO_PERM:       errno = EPERM;        return -1;
-	case Result::MKDIR_OK:                errno = 0;            break;
+	case Result::MKDIR_OK:                                      break;
 	}
 	return 0;
 }
@@ -498,7 +496,7 @@ int Libc::Vfs_plugin::stat(char const *path, struct stat *buf)
 
 	switch (_root_dir.stat(path, stat)) {
 	case Result::STAT_ERR_NO_ENTRY: errno = ENOENT; return -1;
-	case Result::STAT_OK:           errno = 0;      break;
+	case Result::STAT_OK:                           break;
 	}
 
 	vfs_stat_to_libc_stat_struct(stat, buf);
@@ -521,7 +519,7 @@ ssize_t Libc::Vfs_plugin::write(Libc::File_descriptor *fd, const void *buf,
 	case Result::WRITE_ERR_INVALID:     errno = EINVAL;      return -1;
 	case Result::WRITE_ERR_IO:          errno = EIO;         return -1;
 	case Result::WRITE_ERR_INTERRUPT:   errno = EINTR;       return -1;
-	case Result::WRITE_OK:              errno = 0;           break;
+	case Result::WRITE_OK:                                   break;
 	}
 
 	handle->advance_seek(out_count);
@@ -545,7 +543,7 @@ ssize_t Libc::Vfs_plugin::read(Libc::File_descriptor *fd, void *buf,
 	case Result::READ_ERR_INVALID:     errno = EINVAL;      PERR("A3"); return -1;
 	case Result::READ_ERR_IO:          errno = EIO;         PERR("A4"); return -1;
 	case Result::READ_ERR_INTERRUPT:   errno = EINTR;       PERR("A5"); return -1;
-	case Result::READ_OK:              errno = 0;           break;
+	case Result::READ_OK:                                               break;
 	}
 
 	handle->advance_seek(out_count);
@@ -573,7 +571,7 @@ ssize_t Libc::Vfs_plugin::getdirentries(Libc::File_descriptor *fd, char *buf,
 
 	switch (handle->ds().dirent(fd->fd_path, index, dirent_out)) {
 	case Result::DIRENT_ERR_INVALID_PATH: /* XXX errno */ return -1;
-	case Result::DIRENT_OK:               errno = 0;      break;
+	case Result::DIRENT_OK:                               break;
 	}
 
 	/*
@@ -713,7 +711,7 @@ int Libc::Vfs_plugin::ioctl(Libc::File_descriptor *fd, int request, char *argp)
 	switch (handle->fs().ioctl(handle, opcode, arg, out)) {
 	case Vfs::File_io_service::IOCTL_ERR_INVALID: errno = EINVAL; return -1;
 	case Vfs::File_io_service::IOCTL_ERR_NOTTY:   errno = ENOTTY; return -1;
-	case Vfs::File_io_service::IOCTL_OK:          errno = 0;      break;
+	case Vfs::File_io_service::IOCTL_OK:                          break;
 	}
 
 	/*
@@ -782,7 +780,7 @@ int Libc::Vfs_plugin::ftruncate(Libc::File_descriptor *fd, ::off_t length)
 	switch (handle->fs().ftruncate(handle, length)) {
 	case Result::FTRUNCATE_ERR_NO_PERM:   errno = EPERM; return -1;
 	case Result::FTRUNCATE_ERR_INTERRUPT: errno = EINTR; return -1;
-	case Result::FTRUNCATE_OK:            errno = 0;     break;
+	case Result::FTRUNCATE_OK:                           break;
 	}
 	return 0;
 }
@@ -842,7 +840,7 @@ int Libc::Vfs_plugin::symlink(const char *oldpath, const char *newpath)
 	case Result::SYMLINK_ERR_NO_ENTRY:      errno = ENOENT;       return -1;
 	case Result::SYMLINK_ERR_NAME_TOO_LONG: errno = ENAMETOOLONG; return -1;
 	case Result::SYMLINK_ERR_NO_PERM:       errno = ENOSYS;       return -1;
-	case Result::SYMLINK_OK:                errno = 0;            break;
+	case Result::SYMLINK_OK:                                      break;
 	}
 	return 0;
 }
@@ -856,7 +854,7 @@ ssize_t Libc::Vfs_plugin::readlink(const char *path, char *buf, size_t buf_size)
 
 	switch (_root_dir.readlink(path, buf, buf_size, out_len)) {
 	case Result::READLINK_ERR_NO_ENTRY: errno = ENOENT; return -1;
-	case Result::READLINK_OK:           errno = 0;      break;
+	case Result::READLINK_OK:                           break;
 	};
 
 	return out_len;
@@ -876,7 +874,7 @@ int Libc::Vfs_plugin::unlink(char const *path)
 	switch (_root_dir.unlink(path)) {
 	case Result::UNLINK_ERR_NO_ENTRY: errno = ENOENT; return -1;
 	case Result::UNLINK_ERR_NO_PERM:  errno = EPERM;  return -1;
-	case Result::UNLINK_OK:           errno = 0;      break;
+	case Result::UNLINK_OK:                           break;
 	}
 	return 0;
 }
@@ -890,7 +888,7 @@ int Libc::Vfs_plugin::rename(char const *from_path, char const *to_path)
 	case Result::RENAME_ERR_NO_ENTRY: errno = ENOENT; return -1;
 	case Result::RENAME_ERR_CROSS_FS: errno = EXDEV;  return -1;
 	case Result::RENAME_ERR_NO_PERM:  errno = EPERM;  return -1;
-	case Result::RENAME_OK:           errno = 0;      break;
+	case Result::RENAME_OK:                           break;
 	}
 	return 0;
 }