extendedFILE

- enable extended FILE facility usage

Synopsis

$ ulimit -n N_file_descriptors
$ LD_PRELOAD_32=/usr/lib/extendedFILE.so.1 application [arg...]

Description

The extendedFILE.so.1 is not a library but an enabler of the extended FILE facility.

The extended FILE facility allows 32-bit processes to use any valid file descriptor with the standard I/O (see stdio(3C)) C library functions. Historically, 32-bit applications have been limited to using the first 256 numerical file descriptors for use with standard I/O streams. By using the extended FILE facility this limitation is lifted. Any valid file descriptor can be used with standard I/O. See the NOTES section of enable_extended_FILE_stdio(3C).

The extended FILE facility is enabled from the shell level before an application is launched. The file descriptor limit must also be raised. The syntax for raising the file descriptor limit is

$ ulimit -n max_file_descriptors
$ LD_PRELOAD_32=/usr/lib/extendedFILE.so.1 application [arg...]

where max_file_descriptors is the maximum number of file descriptors desired. See limit(1). The maximum value is the same as the maximum value for open(2).

Environment Variables

The following environment variables control the behavior of the extended FILE facility.

_STDIO_BADFD

This variable takes an integer representing the lowest file descriptor, which will be made unallocatable. This action provides a protection mechanism so that applications that abuse interfaces do not experience silent data corruption. The value must be between 3 and 255 inclusive.

_STDIO_BADFD_SIGNAL

This variable takes an integer or string representing any valid signal. See signal.h(3HEAD) for valid values or strings. This environment variable causes the specified signal to be sent to the application if certain exceptional cases are detected during the use of this facility. The default signal is SIGABRT.

Examples

Example 1 Limit the number of file descriptors and FILE standard I/O structures.

The following example limits the number of file descriptors and FILE standard I/O structures to 1000.

$ ulimit -n 1000
$ LD_PRELOAD_32=/usr/lib/extendedFILE.so.1 application [arg...]

Example 2 Enable the extended FILE facility.

The following example enables the extended FILE facility. See enable_extended_FILE_stdio(3C) for more examples.

$ ulimit -n 1000
$ _STDIO_BADFD=100 _STDIO_BADFD_SIGNAL=SIGABRT \
   LD_PRELOAD_32=/usr/lib/extendedFILE.so.1  \
   application [arg ...]

Example 3 Set up the extended FILE environment and start the application.

The following shell script first sets up the proper extended FILE environment and then starts the application:

#!/bin/sh
if [ $# = 0 ]; then
   echo "usage: $0 application [arguments...]"
   exit 1
fi
ulimit -n 1000
# _STDIO_BADFD=196; export _STDIO_BADFD
# _STDIO_BADFD_SIGNAL=SIGABRT; export _STDIO_BADFD_SIGNAL
LD_PRELOAD_32=/usr/lib/extendedFILE.so.1; export LD_PRELOAD_32
"$@"

Files

/usr/lib/extendedFILE.so.1

enabling library

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

limit(1), open(2), enable_extended_FILE_stdio(3C), fdopen(3C), fopen(3C), popen(3C), signal.h(3HEAD), stdio(3C), attributes(5)

Warnings

The following displayed message

Application violated extended FILE safety mechanism.
Please read the man page for extendedFILE.
Aborting

is an indication that your application is modifying the internal file descriptor field of the FILE structure from standard I/O. Continued use of this extended FILE facility could harm your data. Do not use the extended FILE facility with your application.