posix_fallocate(3) — Linux manual page


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

NAME         top

       posix_fallocate - allocate file space

SYNOPSIS         top

       #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_C_SOURCE >= 200112L

DESCRIPTION         top

       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
       successful 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         top

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

ERRORS         top

       EBADF  fd is not a valid file descriptor, or is not opened for

       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         top

       posix_fallocate() is available since glibc 2.1.94.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface         Attribute     Value                   │
       │posix_fallocate() │ Thread safety │ MT-Safe (but see NOTES) │

CONFORMING TO         top


       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
       implementation 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         top

       In the glibc implementation, posix_fallocate() is implemented using
       the fallocate(2) system call, which is MT-safe.  If the underlying
       filesystem 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
         function 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         top

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

COLOPHON         top

       This page is part of release 5.08 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

GNU                              2017-09-15               POSIX_FALLOCATE(3)

Pages that refer to this page: fallocate(1)rsync(1)arm_fadvise(2)arm_fadvise64_64(2)fadvise64(2)fadvise64_64(2)fallocate(2)lseek(2)posix_fadvise(2)