Pádraig Brady wrote: > So in summary I would do: > > 1. by default always use internal PRNG seeded with getpid() > 2. if --random-source specified read all random data from there > > Note 2 will allow one to specify /dev/zero if desired. > We could seed our PRNG with /dev/urandom if available, but > that complication is not necessary I think for this problem.
Simple patch attached to do as above. Note I've left `sort -R` and `shuf` reading /dev/urandom as before. This shows the speedup on my system with default options: $ shred -v -n3 t shred: t: pass 1/3 (random)... shred: t: pass 1/3 (random)...8.3MiB/1000MiB 0% shred: t: pass 1/3 (random)...17MiB/1000MiB 1% shred: t: pass 1/3 (random)...32MiB/1000MiB 3% ... $ time ./shred -v t ./shred: t: pass 1/3 (random)... ./shred: t: pass 1/3 (random)...116MiB/1000MiB 11% ./shred: t: pass 1/3 (random)...216MiB/1000MiB 21% ./shred: t: pass 1/3 (random)...340MiB/1000MiB 34% ... cheers, Pádraig.
>From 005277ea7c645ae2bc1d0e88b1681b55c44348af Mon Sep 17 00:00:00 2001 From: =?utf-8?q?P=C3=A1draig=20Brady?= <p...@draigbrady.com> Date: Mon, 6 Apr 2009 08:42:15 +0100 Subject: [PATCH] shred: speed up random passes by not using /dev/urandom Suggestion from Steven Schveighoffer at: http://savannah.gnu.org/patch/?6797 * gl/lib/randread.c: Don't default to using /dev/urandom * gl/lib/randread.h: Expose DEFAULT_RANDOM_FILE define * src/shred.c: Use internal PRNG by default * src/shuf.c: Explicitly choose DEFAULT_RANDOM_FILE * src/sort.c: ditto --- NEWS | 7 +++++++ THANKS | 1 + gl/lib/randread.c | 24 +++++++----------------- gl/lib/randread.h | 6 ++++++ src/shred.c | 2 +- src/shuf.c | 2 +- src/sort.c | 2 +- 7 files changed, 24 insertions(+), 20 deletions(-) diff --git a/NEWS b/NEWS index 7fdbd08..57b5361 100644 --- a/NEWS +++ b/NEWS @@ -7,6 +7,13 @@ GNU coreutils NEWS -*- outline -*- ls now aligns output correctly in the presence of abbreviated month names from the locale database that have differing widths. +** Changes in behavior + + shred: now uses its internal random data generator by default, which + means the 3 random passes it does by default should proceed at the + speed of the disk. Previously /dev/urandom was used if available, + which is relatively slow on GNU/Linux systems at least. + * Noteworthy changes in release 7.2 (2009-03-31) [stable] ** New features diff --git a/THANKS b/THANKS index 11f43ac..6a918a4 100644 --- a/THANKS +++ b/THANKS @@ -525,6 +525,7 @@ Steve McIntyre st...@einval.com Steve Ward plane...@gmail.com Steven G. Johnson stev...@alum.mit.edu Steven Mocking u...@quicknet.nl +Steven Schveighoffer schvei...@yahoo.com Steven P Watson ste...@magelico.net Stuart Kemp sk...@peter.bmc.com Stuart Shelton stu...@shelton.me diff --git a/gl/lib/randread.c b/gl/lib/randread.c index b81a451..798d4e0 100644 --- a/gl/lib/randread.c +++ b/gl/lib/randread.c @@ -50,10 +50,6 @@ # define ALIGNED_POINTER(ptr, type) ((size_t) (ptr) % alignof (type) == 0) #endif -#ifndef DEFAULT_RANDOM_FILE -# define DEFAULT_RANDOM_FILE "/dev/urandom" -#endif - /* The maximum buffer size used for reads of random data. Using the value 2 * ISAAC_BYTES makes this the largest power of two that would not otherwise cause struct randread_source to grow. */ @@ -62,10 +58,8 @@ /* A source of random data for generating random buffers. */ struct randread_source { - /* Stream to read random bytes from. If null, the behavior is - undefined; the current implementation uses ISAAC in this case, - but this is for old-fashioned implementations that lack - /dev/urandom and callers should not rely on this. */ + /* Stream to read random bytes from. If null, the current + implementation uses an internal PRNG (ISAAC). */ FILE *source; /* Function to call, and its argument, if there is an input error or @@ -147,18 +141,14 @@ randread_new (char const *name, size_t bytes_bound) return simple_new (NULL, NULL); else { - char const *file_name = (name ? name : DEFAULT_RANDOM_FILE); - FILE *source = fopen_safer (file_name, "rb"); + FILE *source = NULL; struct randread_source *s; - if (! source) - { - if (name) - return NULL; - file_name = NULL; - } + if (name) + if (! (source = fopen_safer (name, "rb"))) + return NULL; - s = simple_new (source, file_name); + s = simple_new (source, name); if (source) setvbuf (source, s->buf.c, _IOFBF, MIN (sizeof s->buf.c, bytes_bound)); diff --git a/gl/lib/randread.h b/gl/lib/randread.h index 5f044bd..902251e 100644 --- a/gl/lib/randread.h +++ b/gl/lib/randread.h @@ -22,6 +22,12 @@ # include <stddef.h> +#ifndef DEFAULT_RANDOM_FILE +/* Note /dev/urandom is not designed as a bulk random data source as + it's quite slow and also it depletes the entropy of the system. */ +# define DEFAULT_RANDOM_FILE "/dev/urandom" +#endif + struct randread_source; struct randread_source *randread_new (char const *, size_t); diff --git a/src/shred.c b/src/shred.c index 6ed4daa..69bc226 100644 --- a/src/shred.c +++ b/src/shred.c @@ -167,7 +167,7 @@ Mandatory arguments to long options are mandatory for short options too.\n\ printf (_("\ -f, --force change permissions to allow writing if necessary\n\ -n, --iterations=N overwrite N times instead of the default (%d)\n\ - --random-source=FILE get random bytes from FILE (default /dev/urandom)\n\ + --random-source=FILE get random bytes from FILE\n\ -s, --size=N shred this many bytes (suffixes like K, M, G accepted)\n\ "), DEFAULT_PASSES); fputs (_("\ diff --git a/src/shuf.c b/src/shuf.c index 977eedc..cf9d27b 100644 --- a/src/shuf.c +++ b/src/shuf.c @@ -245,7 +245,7 @@ main (int argc, char **argv) size_t hi_input = 0; size_t head_lines = SIZE_MAX; char const *outfile = NULL; - char *random_source = NULL; + const char *random_source = DEFAULT_RANDOM_FILE; char eolbyte = '\n'; char **input_lines = NULL; diff --git a/src/sort.c b/src/sort.c index 5b63a25..8ce3f00 100644 --- a/src/sort.c +++ b/src/sort.c @@ -3037,7 +3037,7 @@ main (int argc, char **argv) int c = 0; char checkonly = 0; bool mergeonly = false; - char *random_source = NULL; + const char *random_source = DEFAULT_RANDOM_FILE; bool need_random = false; size_t nfiles = 0; bool posixly_correct = (getenv ("POSIXLY_CORRECT") != NULL); -- 1.5.3.6
_______________________________________________ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
