ptsnamefd

Ptsnamefd is a C library function used with pseudo-terminals (PTYs) to obtain the slave side of a PTY pair from the master’s file descriptor. It serves as a convenience alternative to the traditional PTY helpers by returning an open file descriptor for the slave device rather than a path string.

Overview

- Purpose: Given a master PTY file descriptor, ptsnamefd provides access to the associated slave PTY via a file descriptor, enabling direct I/O without requiring the caller to resolve or open a device path.

- Relationship to other APIs: It complements standard PTY interfaces such as ptsname (which returns the slave’s path) and ptsname_r (a thread-safe variant). It sits alongside posix_openpt, grantpt, and unlockpt in the PTY workflow.

Availability and portability

- Nature: Ptsnamefd is not part of the POSIX standard and is implemented as a library extension on some systems.

- Implementations: It is available in certain libc implementations (for example, some Linux and BSD environments) but is not universally portable. Programs intended for broad portability should rely on POSIX-standard APIs such as posix_openpt, grantpt, unlockpt, and ptsname_r where possible.

Usage notes

- Typical usage involves obtaining a master PTY file descriptor (for example via posix_openpt), performing any necessary grant/unlock steps, and then invoking ptsnamefd to obtain a slave FD for direct use.

- Error handling follows standard C conventions: a failure returns an error indication (such as -1) and sets errno.

See also

- ptsname, ptsname_r

- posix_openpt

- grantpt, unlockpt

Limitations

- Because it is an extension, code using ptsnamefd may require conditional compilation or alternative code paths on platforms that do not provide it. When portability is a concern, prefer the standard PTY APIs and their documented behavior.