explain_poll man page

explain_poll — explain poll(2) errors

Synopsis

#include <libexplain/poll.h>

const char *explain_poll(struct pollfd *fds, int nfds, int timeout);
const char *explain_errno_poll(int errnum, struct pollfd *fds, int nfds, int timeout);
void explain_message_poll(char *message, int message_size, struct pollfd *fds, int nfds, int timeout);
void explain_message_errno_poll(char *message, int message_size, int errnum, struct pollfd *fds, int nfds, int timeout);

Description

These functions may be used to obtain explanations for errors returned by the poll(2) system call.

explain_poll

const char *explain_poll(struct pollfd *fds, int nfds, int timeout);

The explain_poll function is used to obtain an explanation of an error returned by the poll(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

fds
The original fds, exactly as passed to the poll(2) system call.
nfds
The original nfds, exactly as passed to the poll(2) system call.
timeout
The original timeout, exactly as passed to the poll(2) system call.
Returns:
The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:

int result = poll(fds, nfds, timeout);
if (result < 0)

{

fprintf(stderr, "%s\n", explain_poll(fds, nfds, timeout));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_poll_or_die(3) function.

explain_errno_poll

const char *explain_errno_poll(int errnum, struct pollfd *fds, int nfds, int timeout);

The explain_errno_poll function is used to obtain an explanation of an error returned by the poll(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

errnum
The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.
fds
The original fds, exactly as passed to the poll(2) system call.
nfds
The original nfds, exactly as passed to the poll(2) system call.
timeout
The original timeout, exactly as passed to the poll(2) system call.
Returns:
The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:

int result = poll(fds, nfds, timeout);
if (result < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_poll(err, fds, nfds, timeout));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_poll_or_die(3) function.

explain_message_poll

void explain_message_poll(char *message, int message_size, struct pollfd *fds, int nfds, int timeout);

The explain_message_poll function is used to obtain an explanation of an error returned by the poll(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

message
The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.
message_size
The size in bytes of the location in which to store the returned message.
fds
The original fds, exactly as passed to the poll(2) system call.
nfds
The original nfds, exactly as passed to the poll(2) system call.
timeout
The original timeout, exactly as passed to the poll(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:

int result = poll(fds, nfds, timeout);
if (result < 0)

{
    char message[3000];

explain_message_poll(message, sizeof(message), fds, nfds, timeout);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_poll_or_die(3) function.

explain_message_errno_poll

void explain_message_errno_poll(char *message, int message_size, int errnum, struct pollfd *fds, int nfds, int timeout);

The explain_message_errno_poll function is used to obtain an explanation of an error returned by the poll(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

message
The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.
message_size
The size in bytes of the location in which to store the returned message.
errnum
The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.
fds
The original fds, exactly as passed to the poll(2) system call.
nfds
The original nfds, exactly as passed to the poll(2) system call.
timeout
The original timeout, exactly as passed to the poll(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:

int result = poll(fds, nfds, timeout);
if (result < 0)

{
    int err = errno;
    char message[3000];

explain_message_errno_poll(message, sizeof(message), err, fds, nfds, timeout);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_poll_or_die(3) function.

See Also

poll(2)
wait for some event on a file descriptor
explain_poll_or_die(3)
wait for some event on a file descriptor and report errors

Referenced By

explain(3), explain_poll_or_die(3).