Man Linux: Main Page and Category List

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 0.19
       Copyright (C) 2009 Peter Miller

                                                              explain_pread(3)