Provided by: libexplain-dev_1.4.D001-8_amd64 bug

NAME

       explain_pread - explain pread(2) errors

SYNOPSIS

       #include <libexplain/pread.h>
       const char *explain_pread(int fildes, void *data, size_t data_size, off_t offset);
       const char *explain_errno_pread(int errnum, int fildes, void *data, size_t data_size,
       off_t offset);
       void explain_message_pread(char *message, int message_size, int fildes, void *data, size_t
       data_size, off_t offset);
       void explain_message_errno_pread(char *message, int message_size, int errnum, int fildes,
       void *data, size_t data_size, off_t offset);

DESCRIPTION

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

   explain_pread
       const char *explain_pread(int fildes, void *data, size_t data_size, off_t offset);

       The  explain_pread  function  is used to obtain an explanation of an error returned by the
       pread(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.

       fildes  The original fildes, exactly as passed to the pread(2) system call.

       data    The original data, exactly as passed to the pread(2) system call.

       data_size
               The original data_size, exactly as passed to the pread(2) system call.

       offset  The original offset, exactly as passed to the pread(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:
              ssize_t result = pread(fildes, data, data_size, offset);
              if (result < 0)
              {
                  fprintf(stderr, "%s\n", explain_pread(fildes, data, data_size, offset));
                  exit(EXIT_FAILURE);
              }

       The above code example is available pre‐packaged as the explain_pread_or_die(3) function.

   explain_errno_pread
       const char *explain_errno_pread(int errnum, int fildes, void *data, size_t data_size,
       off_t offset);

       The  explain_errno_pread function is used to obtain an explanation of an error returned by
       the  pread(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.

       fildes  The original fildes, exactly as passed to the pread(2) system call.

       data    The original data, exactly as passed to the pread(2) system call.

       data_size
               The original data_size, exactly as passed to the pread(2) system call.

       offset  The original offset, exactly as passed to the pread(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:
              ssize_t result = pread(fildes, data, data_size, offset);
              if (result < 0)
              {
                  int err = errno;
                  fprintf(stderr, "%s\n", explain_errno_pread(err, fildes, data, data_size,
                  offset));
                  exit(EXIT_FAILURE);
              }

       The above code example is available pre‐packaged as the explain_pread_or_die(3) function.

   explain_message_pread
       void explain_message_pread(char *message, int message_size, int fildes, void *data, size_t
       data_size, off_t offset);

       The explain_message_pread function is used to obtain an explanation of an  error  returned
       by  the  pread(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.

       fildes  The original fildes, exactly as passed to the pread(2) system call.

       data    The original data, exactly as passed to the pread(2) system call.

       data_size
               The original data_size, exactly as passed to the pread(2) system call.

       offset  The original offset, exactly as passed to the pread(2) system call.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              ssize_t result = pread(fildes, data, data_size, offset);
              if (result < 0)
              {
                  char message[3000];
                  explain_message_pread(message, sizeof(message), fildes, data, data_size,
                  offset);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       The above code example is available pre‐packaged as the explain_pread_or_die(3) function.

   explain_message_errno_pread
       void explain_message_errno_pread(char *message, int message_size, int errnum, int fildes,
       void *data, size_t data_size, off_t offset);

       The  explain_message_errno_pread  function  is  used  to obtain an explanation of an error
       returned by the pread(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.

       fildes  The original fildes, exactly as passed to the pread(2) system call.

       data    The original data, exactly as passed to the pread(2) system call.

       data_size
               The original data_size, exactly as passed to the pread(2) system call.

       offset  The original offset, exactly as passed to the pread(2) system call.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              ssize_t result = pread(fildes, data, data_size, offset);
              if (result < 0)
              {
                  int err = errno;
                  char message[3000];
                  explain_message_errno_pread(message, sizeof(message), err, fildes, data,
                  data_size, offset);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       The above code example is available pre‐packaged as the explain_pread_or_die(3) function.

SEE ALSO

       pread(2)
               read from or write to a file descriptor at a given offset

       explain_pread_or_die(3)
               read from or write to a file descriptor at a given offset and report errors

COPYRIGHT

       libexplain version 1.4
       Copyright (C) 2009 Peter Miller

                                                                                 explain_pread(3)