explain_shmctl man page

explain_shmctl — explain shmctl(2) errors

Synopsis

#include <libexplain/shmctl.h>

const char *explain_shmctl(int shmid, int command, struct shmid_ds *data);
const char *explain_errno_shmctl(int errnum, int shmid, int command, struct shmid_ds *data);
void explain_message_shmctl(char *message, int message_size, int shmid, int command, struct shmid_ds *data);
void explain_message_errno_shmctl(char *message, int message_size, int errnum, int shmid, int command, struct shmid_ds *data);

Description

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

explain_shmctl

const char *explain_shmctl(int shmid, int command, struct shmid_ds *data);

The explain_shmctl function is used to obtain an explanation of an error returned by the shmctl(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.

shmid
The original shmid, exactly as passed to the shmctl(2) system call.
command
The original command, exactly as passed to the shmctl(2) system call.
data
The original data, exactly as passed to the shmctl(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:

if (shmctl(shmid, command, data) < 0)

{

fprintf(stderr, "%s\n", explain_shmctl(shmid, command, data));

    exit(EXIT_FAILURE);
}

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

explain_errno_shmctl

const char *explain_errno_shmctl(int errnum, int shmid, int command, struct shmid_ds *data);

The explain_errno_shmctl function is used to obtain an explanation of an error returned by the shmctl(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.
shmid
The original shmid, exactly as passed to the shmctl(2) system call.
command
The original command, exactly as passed to the shmctl(2) system call.
data
The original data, exactly as passed to the shmctl(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:

if (shmctl(shmid, command, data) < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_shmctl(err, shmid, command, data));

    exit(EXIT_FAILURE);
}

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

explain_message_shmctl

void explain_message_shmctl(char *message, int message_size, int shmid, int command, struct shmid_ds *data);

The explain_message_shmctl function is used to obtain an explanation of an error returned by the shmctl(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.
shmid
The original shmid, exactly as passed to the shmctl(2) system call.
command
The original command, exactly as passed to the shmctl(2) system call.
data
The original data, exactly as passed to the shmctl(2) system call.

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

if (shmctl(shmid, command, data) < 0)

{
    char message[3000];

explain_message_shmctl(message, sizeof(message), shmid, command, data);

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

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

explain_message_errno_shmctl

void explain_message_errno_shmctl(char *message, int message_size, int errnum, int shmid, int command, struct shmid_ds *data);

The explain_message_errno_shmctl function is used to obtain an explanation of an error returned by the shmctl(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.
shmid
The original shmid, exactly as passed to the shmctl(2) system call.
command
The original command, exactly as passed to the shmctl(2) system call.
data
The original data, exactly as passed to the shmctl(2) system call.

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

if (shmctl(shmid, command, data) < 0)

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

explain_message_errno_shmctl(message, sizeof(message), err, shmid, command, data);

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

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

See Also

shmctl(2)
shared memory control
explain_shmctl_or_die(3)
shared memory control and report errors

Referenced By

explain(3), explain_shmctl_or_die(3).