GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


man:posix_fallocate

POSIX_FALLOCATE(3) Linux Programmer's Manual POSIX_FALLOCATE(3)

NAME

     posix_fallocate - allocate file space

SYNOPSIS

     #include <fcntl.h>
     int posix_fallocate(int fd, off_t offset, off_t len);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     posix_fallocate():
         _POSIX_C_SOURCE >= 200112L

DESCRIPTION

     The function posix_fallocate() ensures that disk space is allocated for
     the file referred to by the file descriptor fd for  the  bytes  in  the
     range  starting  at  offset and continuing for len bytes.  After a suc-
     cessful call to posix_fallocate(), subsequent writes to  bytes  in  the
     specified  range  are  guaranteed  not  to fail because of lack of disk
     space.
     If the size of the file is less  than  offset+len,  then  the  file  is
     increased to this size; otherwise the file size is left unchanged.

RETURN VALUE

     posix_fallocate()  returns zero on success, or an error number on fail-
     ure.  Note that errno is not set.

ERRORS

     EBADF  fd is not a valid file descriptor, or is not opened for writing.
     EFBIG  offset+len exceeds the maximum file size.
     EINTR  A signal was caught during execution.
     EINVAL offset  was  less than 0, or len was less than or equal to 0, or
            the underlying filesystem does not support the operation.
     ENODEV fd does not refer to a regular file.
     ENOSPC There is not enough space left on the device containing the file
            referred to by fd.
     ESPIPE fd refers to a pipe.

VERSIONS

     posix_fallocate() is available since glibc 2.1.94.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     +------------------+---------------+-------------------------+
     |Interface         | Attribute     | Value                   |
     +------------------+---------------+-------------------------+
     |posix_fallocate() | Thread safety | MT-Safe (but see NOTES) |
     +------------------+---------------+-------------------------+

CONFORMING TO

     POSIX.1-2001.
     POSIX.1-2008 says that an implementation shall give the EINVAL error if
     len was 0, or offset was less than 0.  POSIX.1-2001 says that an imple-
     mentation shall give the EINVAL error if len is less than 0, or  offset
     was less than 0, and may give the error if len equals zero.

NOTES

     In the glibc implementation, posix_fallocate() is implemented using the
     fallocate(2) system call, which is MT-safe.  If the underlying filesys-
     tem  does not support fallocate(2), then the operation is emulated with
     the following caveats:
  • The emulation is inefficient.
  • There is a race condition where concurrent writes from another thread

or process could be overwritten with null bytes.

  • There is a race condition where concurrent file size increases by

another thread or process could result in a file whose size is

       smaller than expected.
  • If fd has been opened with the O_APPEND or O_WRONLY flags, the func-

tion fails with the error EBADF.

     In general, the emulation is not MT-safe.  On Linux,  applications  may
     use  fallocate(2)  if  they  cannot tolerate the emulation caveats.  In
     general, this is only recommended if the application plans to terminate
     the  operation  if  EOPNOTSUPP  is  returned, otherwise the application
     itself will need to implement a fallback with all the same problems  as
     the emulation provided by glibc.

SEE ALSO

     fallocate(1), fallocate(2), lseek(2), posix_fadvise(2)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

GNU 2017-09-15 POSIX_FALLOCATE(3)

/data/webs/external/dokuwiki/data/pages/man/posix_fallocate.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki