EC
ENOSTR
Linux / POSIXERRORNotableDeviceHIGH confidence

Device Not a Stream

Production Risk

Programming error — wrong API used for the file type.

What this means

ENOSTR (errno 60) is returned when a STREAMS-specific operation is attempted on a file descriptor that is not a STREAMS device.

Why it happens
  1. 1Calling a STREAMS ioctl (I_PUSH, I_POP, etc.) on a regular file or non-STREAMS fd
  2. 2Attempting getmsg()/putmsg() on a non-STREAMS descriptor
How to reproduce

getmsg() on a regular file descriptor.

trigger — this will error
trigger — this will error
int fd = open("/tmp/regular_file", O_RDWR);
struct strbuf ctrl = {0}, data = {0};
int flags = 0;
getmsg(fd, &ctrl, &data, &flags);
// Returns -1, errno = ENOSTR

expected output

getmsg: Device not a stream (ENOSTR)

Fix

Ensure the fd is a STREAMS device

WHEN Before calling getmsg/putmsg or STREAMS ioctls

Ensure the fd is a STREAMS device
// Check if fd is a STREAMS device
if (isastream(fd)) {
  getmsg(fd, &ctrl, &data, &flags);
} else {
  // Use regular read/write instead
  read(fd, buf, sizeof(buf));
}

Why this works

isastream() returns non-zero if the fd is a STREAMS device.

Sources
Official documentation ↗

Linux Programmer Manual errno(3)

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