Copyright Digital Equipment Corp. All rights reserved.
Description
When the _USE_STD_STAT feature-test macro is not enabled, the
legacy stat structure is used. When _USE_STD_STAT is enabled, the
X/Open standard-compliant stat structure is used.
Legacy stat Structure
With the _USE_STD_STAT feature-test macro defined to DISABLE, the
following legacy stat structure is used:
Member Type Definition
st_dev dev_t Pointer to the physical device name
st_ino[3] ino_t Three words to receive the file ID
st_mode mode_t File "mode" (prot, dir, . . . )
st_nlink nlink_t For UNIX system compatibility only
st_uid uid_t Owner user ID
st_gid gid_t Group member: from st_uid
st_rdev dev_t UNIX system compatibility - always 0
st_size off_t File size, in bytes. For st_size to
report a correct value, you need to
flush both the C RTL and RMS buffers.
st_atime time_t File access time; always the same as
st_mtime
st_mtime time_t Last modification time
st_ctime time_t File creation time
st_fab_rfm char Record format
st_fab_rat char Record attributes
st_fab_fsz char Fixed header size
st_fab_mrs unsigned Record size
The types dev_t, ino_t, off_t, mode_t, nlink_t, uid_t, gid_t, and
time_t, are defined in the <stat.h> header file. However, when
compiling for compatibility (/DEFINE=_DECC_V4_SOURCE), only dev_
t, ino_t, and off_t are defined.
The off_t data type is either a 32-bit or 64-bit integer. The 64-
bit interface allows for file sizes greater than 2 GB, and can be
selected at compile time by defining the _LARGEFILE feature-test
macro as follows:
CC/DEFINE=_LARGEFILE
As of OpenVMS Version 7.0, times are given in seconds since the
Epoch (00:00:00 GMT, January 1, 1970).
The st_mode structure member is the status information mode
defined in the <stat.h> header file. The st_mode bits are
described as follows:
Bits Constant Definition
0170000 S_IFMT Type of file
0040000 S_IFDIR Directory
0020000 S_IFCHR Character special
0060000 S_IFBLK Block special
0100000 S_IFREG Regular
0030000 S_IFMPC Multiplexed char special
0070000 S_IFMPB Multiplexed block special
0004000 S_ISUID Set user ID on execution
0002000 S_ISGID Set group ID on execution
0001000 S_ISVTX Save swapped text even after use
0000400 S_IREAD Read permission, owner
0000200 S_IWRITE Write permission, owner
0000100 S_IEXEC Execute/search permission, owner
The stat function does not work on remote network files.
If the file is a record file, the st_size field includes
carriage-control information. Consequently, the st_size value
will not correspond to the number of characters that can be read
from the file.
Also be aware that for st_size to report a correct value, you
need to flush both the C RTL and RMS buffers.
Standard-Compliant stat Structure
With OpenVMS Version 8.2, the _USE_STD_STAT feature-test macro
and standard-compliant stat structure are introduced in support
of UNIX compatibility.
With _USE_STD_STAT defined to ENABLE, you get the following
behavior:
o Old struct stat definitions
Old definitions of struct stat are obsolete. You must
recompile your applications to access the new features.
Existing applications will continue to access the old
definitions and functions unless they are recompiled to use
the new features.
o Function variants
Calls to stat, fstat, lstat, and ftw accept pointers to
structures of the new type. Calls to these functions are
mapped to the new library entries __std_stat, __std_fstat,
__std_lstat, and __std_ftw, respectively.
o Compatibilities with other feature macros
_DECC_V4_SOURCE source-code compatibility is not supported.
You must not enable _DECC_V4_SOURCE and _USE_STD_STAT at the
same time.
_VMS_V6_SOURCE binary compatibility is not supported. You must
not enable _VMS_V6_SOURCE and _USE_STD_STAT at the same time.
As a result, only UTC (rather than local-time) is supported
for the time_t fields.
o Type changes
The following type changes are in effect:
- 32-bit gid type gid_t is used. _DECC_SHORT_GID_T is
unsupported.
- _LARGEFILE offsets are used. off_t is forced to 64 bits.
- Type ino_t, representing the file number, is an unsigned
int quadword (64 bits). Previously, it was an unsigned
short.
- Type dev_t, representing the device id, is an unsigned int
quadword (64 bits). Previously, it was a 32-bit character
pointer. The new type is standard because it is arithmetic.
- Types blksize_t and blkcnt_t are added and defined as
unsigned int quadwords (64 bits).
o Structure member Changes
- Two members are added to struct stat:
blksize_t st_blksize;
blkcnt_t st_blocks;
According to the X/Open standard, st_blksize is the
filesystem-specific preferred I/O blocksize for this file.
On OpenVMS systems, st_blksize is set to the device buffer
size multiplied by the disk cluster size. st_blocks is set
to the allocated size of the file, in blocks. The blocksize
used to calculate st_blocks is not necessarily the same as
st_blksize and, in most cases, will not be the same.
- In struct stat, member st_ino is of type ino_t. In previous
C RTL versions, it was of type ino_t [3] (array of 3 ino_
t). Since ino_t has changed from a word to a quadword,
the size of this member has increased by one word. The
principal significance of this change is that it makes st_
ino a scalar, which is how most open source applications
define it.
- The new definition of ino_t also affects applications
that include the <dirent.h> header file. In struct dirent,
member d_ino changes in the same way as the st_ino member
of struct stat in <stat.h>.
- Several macros that are not part of any standard were
introduced in <stat.h> to facilitate access to the
constituent parts of ino_t values:
S_INO_NUM(ino), S_INO_SEQ(ino), and S_INO_RVN(ino)
return the FILES-11 file number, sequence number, and
relative volume number of ino, respectively, as unsigned
shorts.
S_INO_RVN_RVN(ino) returns the byte of the RVN field
containing the relative volume number;
S_INO_RVN_NMX(ino) returns the byte of the RVN field
containing the file number extension.
Although individual components can be broken out like this,
they are not part of the X/Open standard and should not be
relied on in portable applications.
o Semantic changes
Values of type dev_t are now unique for each device across
clusters. An algorithm based on device name and allocation
class or SCSSYSTEMID (for single-pathed devices) calculates
the device id value having these characteristics, an X/Open
standard requirement. Typically, the combination of file
number and device id uniquely identifies a file in a cluster.
This change affects stat structure members st_dev and st_rdev.
For compatibility with previous releases, st_rdev is set to
either 0 or st_dev.
NOTE (Integrity servers, Alpha)
On OpenVMS Alpha and Integrity server systems, the stat,
fstat, utime, and utimes functions have been enhanced to
take advantage of the new file-system support for POSIX
compliant file timestamps.
This support is available only on ODS-5 devices on OpenVMS
Alpha systems beginning with a version of OpenVMS Alpha
after Version 7.3.
Before this change, the stat and fstat functions were
setting the values of the st_ctime, st_mtime, and st_atime
fields based on the following file attributes:
st_ctime - ATR$C_CREDATE (file creation time)
st_mtime - ATR$C_REVDATE (file revision time)
st_atime - was always set to st_mtime because no support
for file access time was available
Also, for the file-modification time, utime and utimes were
modifying the ATR$C_REVDATE file attribute, and ignoring the
file-access-time argument.
After the change, for a file on an ODS-5 device, the stat
and fstat functions set the values of the st_ctime, st_
mtime, and st_atime fields based on the following new file
attributes:
st_ctime - ATR$C_ATTDATE (last attribute modification
time)
st_mtime - ATR$C_MODDATE (last data modification time)
st_atime - ATR$C_ACCDATE (last access time)
If ATR$C_ACCDATE is zero, as on an ODS-2 device, the stat
and fstat functions set st_atime to st_mtime.
For the file-modification time, the utime and utimes
functions modify both the ATR$C_REVDATE and ATR$C_MODDATE
file attributes. For the file-access time, these functions
modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_
MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device
has no effect.
For compatibility, the old behavior of stat, fstat, utime,
and utimes remains the default, regardless of the kind of
device.
The new behavior must be explicitly enabled by defining
the DECC$EFS_FILE_TIMESTAMPS logical name to ENABLE before
invoking the application. Setting this logical does not
affect the behavior of stat, fstat, utime, and utimes for
files on an ODS-2 device.