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glibc  2.9
Functions
posix_fallocate.c File Reference
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/statfs.h>
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Functions

int posix_fallocate (int fd, __off_t offset, __off_t len)

Function Documentation

int posix_fallocate ( int  fd,
__off_t  offset,
__off_t  len 
)

Definition at line 28 of file posix_fallocate.c.

{
  struct stat64 st;
  struct statfs f;

  /* `off_t' is a signed type.  Therefore we can determine whether
     OFFSET + LEN is too large if it is a negative value.  */
  if (offset < 0 || len < 0)
    return EINVAL;
  if (offset + len < 0)
    return EFBIG;

  /* First thing we have to make sure is that this is really a regular
     file.  */
  if (__fxstat64 (_STAT_VER, fd, &st) != 0)
    return EBADF;
  if (S_ISFIFO (st.st_mode))
    return ESPIPE;
  if (! S_ISREG (st.st_mode))
    return ENODEV;

  if (len == 0)
    {
      if (st.st_size < offset)
       {
         int ret = __ftruncate (fd, offset);

         if (ret != 0)
           ret = errno;
         return ret;
       }
      return 0;
    }

  /* We have to know the block size of the filesystem to get at least some
     sort of performance.  */
  if (__fstatfs (fd, &f) != 0)
    return errno;

  /* Try to play safe.  */
  if (f.f_bsize == 0)
    f.f_bsize = 512;

  /* Write something to every block.  */
  for (offset += (len - 1) % f.f_bsize; len > 0; offset += f.f_bsize)
    {
      len -= f.f_bsize;

      if (offset < st.st_size)
       {
         unsigned char c;
         ssize_t rsize = __pread (fd, &c, 1, offset);

         if (rsize < 0)
           return errno;
         /* If there is a non-zero byte, the block must have been
            allocated already.  */
         else if (rsize == 1 && c != 0)
           continue;
       }

      if (__pwrite (fd, "", 1, offset) != 1)
       return errno;
    }

  return 0;
}

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