PC Extra Super CD 1998 January/PCPLUS131.iso/DJGPP/V2/DJLSR201.ZIP/src/libc/posix/sys/stat/djbits.txh

Text File | 1996-09-11 | 5.6 KB | 169 lines

@node _djstat_flags, stdio
@subheading Syntax

@example
#include <sys/stat.h>

extern unsigned short   _djstat_flags;
@end example

This variable contains bits for some fields of struct stat which are
expensive to compute under DOS.  Any such computation is only done by
@ref{stat} or @ref{fstat} if the corresponding bit in
@code{_djstat_flags} is @emph{cleared}.  By default, all the bits are
cleared, so applications which don't care, automagically get a full
version, possibly at a price of performance.  To get the fastest
possible @code{f?stat()} for your application, clear only the bits
which you need and set all the others.

The following bits are currently defined:

@table @code

@item _STAT_INODE

Causes @code{f?stat()} to compute the @code{st_ino} (inode number) field.

@item _STAT_EXEC_EXT

Tells @code{f?stat()} to compute the execute access bit from extension.

@item _STAT_EXEC_MAGIC

Tells @code{f?stat()} to compute the execute access bit from magic
signature (the first two bytes of the file, see @ref{_is_executable}.
Note that if _STAT_EXEC_MAGIC is set, but _STAT_EXEC_EXT is not, some
files which shouldn't be flagged as executables (e.g., COFF *.o object
files) will have their execute bit set, because they have the magic
number signature at their beginning.  Therefore, only use the above
combination if you want to debug the list of extensions provided in
is_exec.c file.

@item _STAT_DIRSIZE

Causes @code{stat} to compute directory size by counting the number of its
entries (unless some friendly network redirector brought a true directory
size with it).  Also computes the number of subdirectories and sets the
number of links @code{st_nlink} field.

@item _STAT_ROOT_TIME

Causes @code{stat()} to try to get time stamp of root directory from its
volume label entry, if there is one.

@item _STAT_WRITEBIT

Tells @code{fstat()} that file's write access bit is required (this could
be a problem only under some versions of Novell Netware).

@end table

Note that if you set a bit, some failure bits in @ref{_djstat_fail_bits}
might not be set, because some computations which report failures are only
done when they are required.

@node _djstat_fail_bits, stdio
@subheading Syntax

@example
#include <sys/stat.h>

extern unsigned short   _djstat_fail_bits;
@end example

As proper operation of @ref{stat} and @ref{fstat} depend on
undocumented DOS features, they could fail in some incompatible
environment or a future DOS version.  If they do, the
@code{_djstat_fail_bits} variable will have some of its bits set.
Each bit describes a single feature which was used and failed.  The
function @ref{_djstat_describe_lossage} may be called to print a
human-readable description of the bits which were set by the last call
to @code{f?stat()}.  This should make debugging @code{f?stat()}
failures in an unanticipated environment a lot easier.

The following bits are currently defined:

@table @code

@item _STFAIL_SDA

Indicates that Get SDA call failed.

@item _STFAIL_OSVER

Indicates an unsupported DOS version (less than 3.10 for @code{stat()} or
less than 2.0 for @code{fstat()}).

@item _STFAIL_BADSDA

The pointer to SDA was found to be bogus.

@item _STFAIL_TRUENAME

Indicates that @ref{_truename} function call failed.

@item _STFAIL_HASH

Indicates that the starting cluster of the file is unavailable, and inode
number was computed by hashing its name.

@item _STFAIL_LABEL

The application requested the time stamp of a root dir, but no volume
label was found.

@item _STFAIL_DCOUNT

The number of SDA reported is ridiculously large (probbaly an unsupported
DOS clone).

@item _STFAIL_WRITEBIT

@code{fstat()} was asked to get write access bit of a file, but couldn't.

@item _STFAIL_DEVNO

@code{fstat()} failed to get device number.

@item _STFAIL_BADSFT

An SFT entry for this file was found by @code{fstat()}, but its contents
can't be trusted because it didn't match file size and time stamp as
reported by DOS.

@item _STFAIL_SFTIDX

The SFT index in Job File Table in program's PSP is negative.

@item _STFAIL_SFTNF

The file entry was not found in the SFT array.

@end table

Below are some explanations of terminology and abbreviations used by the
printed messages, which will further clarify the meaning of the above bits
and their descriptions printed by @ref{_djstat_describe_lossage}.

  SDA (Swappable Data Area) -- this is an internal DOS structure.
@code{stat()} uses it to get the full directory entry (including the
starting cluster number) of a file.  The pointer to SDA found by
@code{stat()} is trusted only if we find the pathname of our file at a
specific offset in that SDA.

  SFT (System File Table) -- another internal DOS structure, used in file
operations.  @code{fstat()} uses it to get full information on a file
given its handle.  An SFT entry which is found by @code{fstat()} is only
trusted if it contains files size and time stamp like those returned by
DOS functions 57h and 42h.  Novell NetWare 3.x traps DOS file operations
in such a way they never get to SFT, so some failure messages refer
specifically to Novell.

  Hashing -- the fall-back method of returning a unique inode number for
each file.  It is used whenever the starting cluster of a file couldn't be
reliably determined.  The full pathname of the file is looked up in a
table of files seen earlier (hashing is used to speed the lookup
process).  If found, the inode from the table is returned; this ensures
that a given file will get the same inode number.  Otherwise a new inode
number is invented, recorded in the table and returned to caller.