--- /dev/null
+@node stat-size
+@section stat-size
+
+The @code{stat-size} module provides a small number of macros
+intended for interpreting the file size information in an instance of
+@code{struct stat}.
+
+@c We deliberately don't document DEV_BSIZE (it looks to James
+@c Youngman as if the ST_NBLOCKSIZE macro should be used instead).
+
+@findex ST_NBLOCKS
+@findex ST_NBLOCKSIZE
+@cindex block size
+On POSIX systems, the @code{st_blocks} member of @code{struct stat}
+contains the number of disk blocks occupied by a file. The
+@code{ST_NBLOCKS} macro is used to estimate this quantity on systems
+which don't actually have @code{st_blocks}. Each of these blocks
+contains @code{ST_NBLOCKSIZE} bytes.
+
+@findex ST_BLKSIZE
+The value of @code{ST_NBLOCKSIZE} is often quite small, small enough
+that performing I/O in chunks that size would be inefficient.
+@code{ST_BLKSIZE} is the I/O block size recommended for I/O to this
+file. This is not guaranteed to give optimum performance, but it
+should be reasonably efficient.
--- /dev/null
+/* macros useful in interpreting size-related values in struct stat.
+ Copyright (C) 1989, 1991-2011 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+/*
+ Macros defined by this file (s is an rvalue of type struct stat):
+
+ DEV_BSIZE: The device blocksize. But use ST_NBLOCKSIZE instead.
+ ST_BLKSIZE(s): Preferred (in the sense of best performance) I/O blocksize
+ for the file, in bytes.
+ ST_NBLOCKS(s): Number of blocks in the file, including indirect blocks.
+ ST_NBLOCKSIZE: Size of blocks used when calculating ST_NBLOCKS.
+ */
+#ifndef STAT_SIZE_H
+#define STAT_SIZE_H
+
+/* sys/param.h may define DEV_BSIZE */
+#if HAVE_SYS_PARAM_H
+# include <sys/param.h>
+#endif
+
+
+/* Much of the remainder of this file is not indented consistently
+ with the above, in order to make it easier to see that the text
+ is almost identical to part of the system.h header in coreutils.
+*/
+/* Get or fake the disk device blocksize.
+ Usually defined by sys/param.h (if at all). */
+#if !defined DEV_BSIZE && defined BSIZE
+# define DEV_BSIZE BSIZE
+#endif
+#if !defined DEV_BSIZE && defined BBSIZE /* SGI sys/param.h */
+# define DEV_BSIZE BBSIZE
+#endif
+#ifndef DEV_BSIZE
+# define DEV_BSIZE 4096
+#endif
+
+
+
+/* Extract or fake data from a `struct stat'.
+ ST_BLKSIZE: Preferred I/O blocksize for the file, in bytes.
+ ST_NBLOCKS: Number of blocks in the file, including indirect blocks.
+ ST_NBLOCKSIZE: Size of blocks used when calculating ST_NBLOCKS. */
+#ifndef HAVE_STRUCT_STAT_ST_BLOCKS
+# define ST_BLKSIZE(statbuf) DEV_BSIZE
+ /* coreutils' fileblocks.c also uses BSIZE. */
+# if defined _POSIX_SOURCE || !defined BSIZE
+# define ST_NBLOCKS(statbuf) \
+ ((statbuf).st_size / ST_NBLOCKSIZE + ((statbuf).st_size % ST_NBLOCKSIZE != 0))
+# else
+ /* This definition calls st_blocks, which is in the fileblocks module. */
+# define ST_NBLOCKS(statbuf) \
+ (S_ISREG ((statbuf).st_mode) || S_ISDIR ((statbuf).st_mode) ? \
+ st_blocks ((statbuf).st_size) : 0)
+# endif
+#else
+/* Some systems, like Sequents, return st_blksize of 0 on pipes.
+ Also, when running `rsh hpux11-system cat any-file', cat would
+ determine that the output stream had an st_blksize of 2147421096.
+ Conversely st_blksize can be 2 GiB (or maybe even larger) with XFS
+ on 64-bit hosts. Somewhat arbitrarily, limit the `optimal' block
+ size to SIZE_MAX / 8 + 1. (Dividing SIZE_MAX by only 4 wouldn't
+ suffice, since "cat" sometimes multiplies the result by 4.) If
+ anyone knows of a system for which this limit is too small, please
+ report it as a bug in this code. */
+# define ST_BLKSIZE(statbuf) ((0 < (statbuf).st_blksize \
+ && (statbuf).st_blksize <= ((size_t)-1) / 8 + 1) \
+ ? (statbuf).st_blksize : DEV_BSIZE)
+# if defined hpux || defined __hpux__ || defined __hpux
+ /* HP-UX counts st_blocks in 1024-byte units.
+ This loses when mixing HP-UX and BSD file systems with NFS. */
+# define ST_NBLOCKSIZE 1024
+# else /* !hpux */
+# if defined _AIX && defined _I386
+ /* AIX PS/2 counts st_blocks in 4K units. */
+# define ST_NBLOCKSIZE (4 * 1024)
+# else
+# if defined _CRAY
+# define ST_NBLOCKS(statbuf) \
+ (S_ISREG ((statbuf).st_mode) || S_ISDIR ((statbuf).st_mode) \
+ ? (statbuf).st_blocks * ST_BLKSIZE (statbuf) / ST_NBLOCKSIZE : 0)
+# endif
+# endif
+# endif
+#endif
+
+#ifndef ST_NBLOCKS
+# define ST_NBLOCKS(statbuf) ((statbuf).st_blocks)
+#endif
+
+#ifndef ST_NBLOCKSIZE
+# ifdef S_BLKSIZE
+# define ST_NBLOCKSIZE S_BLKSIZE
+# else
+# define ST_NBLOCKSIZE 512
+# endif
+#endif
+
+#endif /* STAT_SIZE_H */
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