Andreas Dilger wrote:
> I was worried if
> "ls" or something is saving all of the symlink targets in memory that using a
> too-large buffer size would cause excess memory to be allocated for a long
> time.
Good point. careadlinkat.c has a "Shrink BUF before returning it." logic,
but not all similar functions in gnulib do.
As the attached test program shows, some platforms (glibc, Cygwin) have a
special optimization for a shrinking-realloc of the last malloc()ed block.
Other platforms don't have this and a shrinking-realloc moves the data
if there is a significant gain in space by doing so.
Therefore I think it would be good to add a "Shrink BUF before returning it."
logic also to
areadlink-with-size.c
areadlinkat-with-size.c
etc.
Something like this:
diff --git a/lib/areadlink-with-size.c b/lib/areadlink-with-size.c
index eacad3f..364cc08 100644
--- a/lib/areadlink-with-size.c
+++ b/lib/areadlink-with-size.c
@@ -87,6 +87,13 @@ areadlink_with_size (char const *file, size_t size)
if (link_length < buf_size)
{
buffer[link_length] = 0;
+ /* Shrink BUFFER before returning it. */
+ if (link_length + 1 < buf_size)
+ {
+ char *shrinked_buffer = realloc (buffer, link_length + 1);
+ if (shrinked_buffer != NULL)
+ buffer = shrinked_buffer;
+ }
return buffer;
}
#include <stdlib.h>
#include <stdio.h>
int main ()
{
size_t sizes[] = {
1, 2, 3, 4, 5, 6,
7, 8, 9, 11,
15, 16, 17, 23,
31, 32, 33, 45,
63, 64, 65, 91,
127, 128, 129, 181,
255, 256, 257, 362,
511, 512, 513, 724,
1023, 1024, 1025, 1448,
2047, 2048, 2049, 2896,
4095, 4096, 4097, 5793,
8191, 8192, 8193, 11585,
16383, 16384, 16385, 23170,
32767, 32768, 32769, 46341,
65535, 65536, 65537
};
int i;
for (i = 0; i < sizeof (sizes)/sizeof(sizes[0]); i++) {
size_t size = sizes[i];
int j;
for (j = size; j > 0; j--)
{
char *block = malloc (size);
char *new_block = realloc (block, j);
if (new_block == NULL)
abort ();
free (new_block);
if (new_block != block)
break;
}
printf ("initial size = %u: moved in memory for size <= %u\n", (unsigned int) size, (unsigned int) j);
}
}
/*
glibc 2.23, Cygwin:
initial size = 1: moved in memory for size <= 0
initial size = 2: moved in memory for size <= 0
initial size = 3: moved in memory for size <= 0
initial size = 4: moved in memory for size <= 0
initial size = 5: moved in memory for size <= 0
initial size = 6: moved in memory for size <= 0
initial size = 7: moved in memory for size <= 0
initial size = 8: moved in memory for size <= 0
initial size = 9: moved in memory for size <= 0
initial size = 11: moved in memory for size <= 0
initial size = 15: moved in memory for size <= 0
initial size = 16: moved in memory for size <= 0
initial size = 17: moved in memory for size <= 0
initial size = 23: moved in memory for size <= 0
initial size = 31: moved in memory for size <= 0
initial size = 32: moved in memory for size <= 0
initial size = 33: moved in memory for size <= 0
initial size = 45: moved in memory for size <= 0
initial size = 63: moved in memory for size <= 0
initial size = 64: moved in memory for size <= 0
initial size = 65: moved in memory for size <= 0
initial size = 91: moved in memory for size <= 0
initial size = 127: moved in memory for size <= 0
initial size = 128: moved in memory for size <= 0
initial size = 129: moved in memory for size <= 0
initial size = 181: moved in memory for size <= 0
initial size = 255: moved in memory for size <= 0
initial size = 256: moved in memory for size <= 0
initial size = 257: moved in memory for size <= 0
initial size = 362: moved in memory for size <= 0
initial size = 511: moved in memory for size <= 0
initial size = 512: moved in memory for size <= 0
initial size = 513: moved in memory for size <= 0
initial size = 724: moved in memory for size <= 0
initial size = 1023: moved in memory for size <= 0
initial size = 1024: moved in memory for size <= 0
initial size = 1025: moved in memory for size <= 0
initial size = 1448: moved in memory for size <= 0
initial size = 2047: moved in memory for size <= 0
initial size = 2048: moved in memory for size <= 0
initial size = 2049: moved in memory for size <= 0
initial size = 2896: moved in memory for size <= 0
initial size = 4095: moved in memory for size <= 0
initial size = 4096: moved in memory for size <= 0
initial size = 4097: moved in memory for size <= 0
initial size = 5793: moved in memory for size <= 0
initial size = 8191: moved in memory for size <= 0
initial size = 8192: moved in memory for size <= 0
initial size = 8193: moved in memory for size <= 0
initial size = 11585: moved in memory for size <= 0
initial size = 16383: moved in memory for size <= 0
initial size = 16384: moved in memory for size <= 0
initial size = 16385: moved in memory for size <= 0
initial size = 23170: moved in memory for size <= 0
initial size = 32767: moved in memory for size <= 0
initial size = 32768: moved in memory for size <= 0
initial size = 32769: moved in memory for size <= 0
initial size = 46341: moved in memory for size <= 0
initial size = 65535: moved in memory for size <= 0
initial size = 65536: moved in memory for size <= 0
initial size = 65537: moved in memory for size <= 0
FreeBSD 12:
initial size = 1: moved in memory for size <= 0
initial size = 2: moved in memory for size <= 0
initial size = 3: moved in memory for size <= 0
initial size = 4: moved in memory for size <= 0
initial size = 5: moved in memory for size <= 0
initial size = 6: moved in memory for size <= 0
initial size = 7: moved in memory for size <= 0
initial size = 8: moved in memory for size <= 0
initial size = 9: moved in memory for size <= 8
initial size = 11: moved in memory for size <= 8
initial size = 15: moved in memory for size <= 8
initial size = 16: moved in memory for size <= 8
initial size = 17: moved in memory for size <= 16
initial size = 23: moved in memory for size <= 16
initial size = 31: moved in memory for size <= 16
initial size = 32: moved in memory for size <= 16
initial size = 33: moved in memory for size <= 32
initial size = 45: moved in memory for size <= 32
initial size = 63: moved in memory for size <= 48
initial size = 64: moved in memory for size <= 48
initial size = 65: moved in memory for size <= 64
initial size = 91: moved in memory for size <= 80
initial size = 127: moved in memory for size <= 112
initial size = 128: moved in memory for size <= 112
initial size = 129: moved in memory for size <= 128
initial size = 181: moved in memory for size <= 160
initial size = 255: moved in memory for size <= 224
initial size = 256: moved in memory for size <= 224
initial size = 257: moved in memory for size <= 256
initial size = 362: moved in memory for size <= 320
initial size = 511: moved in memory for size <= 448
initial size = 512: moved in memory for size <= 448
initial size = 513: moved in memory for size <= 512
initial size = 724: moved in memory for size <= 640
initial size = 1023: moved in memory for size <= 896
initial size = 1024: moved in memory for size <= 896
initial size = 1025: moved in memory for size <= 1024
initial size = 1448: moved in memory for size <= 1280
initial size = 2047: moved in memory for size <= 1792
initial size = 2048: moved in memory for size <= 1792
initial size = 2049: moved in memory for size <= 2048
initial size = 2896: moved in memory for size <= 2560
initial size = 4095: moved in memory for size <= 3584
initial size = 4096: moved in memory for size <= 3584
initial size = 4097: moved in memory for size <= 4096
initial size = 5793: moved in memory for size <= 5120
initial size = 8191: moved in memory for size <= 7168
initial size = 8192: moved in memory for size <= 7168
initial size = 8193: moved in memory for size <= 8192
initial size = 11585: moved in memory for size <= 10240
initial size = 16383: moved in memory for size <= 14336
initial size = 16384: moved in memory for size <= 14336
initial size = 16385: moved in memory for size <= 14336
initial size = 23170: moved in memory for size <= 14336
initial size = 32767: moved in memory for size <= 14336
initial size = 32768: moved in memory for size <= 14336
initial size = 32769: moved in memory for size <= 14336
initial size = 46341: moved in memory for size <= 14336
initial size = 65535: moved in memory for size <= 14336
initial size = 65536: moved in memory for size <= 14336
initial size = 65537: moved in memory for size <= 14336
Solaris 10:
initial size = 1: moved in memory for size <= 0
initial size = 2: moved in memory for size <= 0
initial size = 3: moved in memory for size <= 0
initial size = 4: moved in memory for size <= 0
initial size = 5: moved in memory for size <= 0
initial size = 6: moved in memory for size <= 0
initial size = 7: moved in memory for size <= 0
initial size = 8: moved in memory for size <= 0
initial size = 9: moved in memory for size <= 8
initial size = 11: moved in memory for size <= 8
initial size = 15: moved in memory for size <= 8
initial size = 16: moved in memory for size <= 8
initial size = 17: moved in memory for size <= 16
initial size = 23: moved in memory for size <= 16
initial size = 31: moved in memory for size <= 24
initial size = 32: moved in memory for size <= 24
initial size = 33: moved in memory for size <= 32
initial size = 45: moved in memory for size <= 32
initial size = 63: moved in memory for size <= 32
initial size = 64: moved in memory for size <= 32
initial size = 65: moved in memory for size <= 32
initial size = 91: moved in memory for size <= 32
initial size = 127: moved in memory for size <= 32
initial size = 128: moved in memory for size <= 32
initial size = 129: moved in memory for size <= 32
initial size = 181: moved in memory for size <= 32
initial size = 255: moved in memory for size <= 32
initial size = 256: moved in memory for size <= 32
initial size = 257: moved in memory for size <= 32
initial size = 362: moved in memory for size <= 32
initial size = 511: moved in memory for size <= 32
initial size = 512: moved in memory for size <= 32
initial size = 513: moved in memory for size <= 32
initial size = 724: moved in memory for size <= 32
initial size = 1023: moved in memory for size <= 32
initial size = 1024: moved in memory for size <= 32
initial size = 1025: moved in memory for size <= 32
initial size = 1448: moved in memory for size <= 32
initial size = 2047: moved in memory for size <= 32
initial size = 2048: moved in memory for size <= 32
initial size = 2049: moved in memory for size <= 32
initial size = 2896: moved in memory for size <= 32
initial size = 4095: moved in memory for size <= 32
initial size = 4096: moved in memory for size <= 32
initial size = 4097: moved in memory for size <= 32
initial size = 5793: moved in memory for size <= 32
initial size = 8191: moved in memory for size <= 32
initial size = 8192: moved in memory for size <= 32
initial size = 8193: moved in memory for size <= 32
initial size = 11585: moved in memory for size <= 32
initial size = 16383: moved in memory for size <= 32
initial size = 16384: moved in memory for size <= 32
initial size = 16385: moved in memory for size <= 32
initial size = 23170: moved in memory for size <= 32
initial size = 32767: moved in memory for size <= 32
initial size = 32768: moved in memory for size <= 32
initial size = 32769: moved in memory for size <= 32
initial size = 46341: moved in memory for size <= 32
initial size = 65535: moved in memory for size <= 32
initial size = 65536: moved in memory for size <= 32
initial size = 65537: moved in memory for size <= 32
MSVC:
initial size = 1: moved in memory for size <= 0
initial size = 2: moved in memory for size <= 0
initial size = 3: moved in memory for size <= 0
initial size = 4: moved in memory for size <= 2
initial size = 5: moved in memory for size <= 5
initial size = 6: moved in memory for size <= 6
initial size = 7: moved in memory for size <= 7
initial size = 8: moved in memory for size <= 8
initial size = 9: moved in memory for size <= 9
initial size = 11: moved in memory for size <= 11
initial size = 15: moved in memory for size <= 15
initial size = 16: moved in memory for size <= 16
initial size = 17: moved in memory for size <= 17
initial size = 23: moved in memory for size <= 23
initial size = 31: moved in memory for size <= 18
initial size = 32: moved in memory for size <= 32
initial size = 33: moved in memory for size <= 0
initial size = 45: moved in memory for size <= 33
initial size = 63: moved in memory for size <= 55
initial size = 64: moved in memory for size <= 64
initial size = 65: moved in memory for size <= 58
initial size = 91: moved in memory for size <= 76
initial size = 127: moved in memory for size <= 122
initial size = 128: moved in memory for size <= 128
initial size = 129: moved in memory for size <= 127
initial size = 181: moved in memory for size <= 178
initial size = 255: moved in memory for size <= 252
initial size = 256: moved in memory for size <= 256
initial size = 257: moved in memory for size <= 254
initial size = 362: moved in memory for size <= 359
initial size = 511: moved in memory for size <= 506
initial size = 512: moved in memory for size <= 512
initial size = 513: moved in memory for size <= 509
initial size = 724: moved in memory for size <= 721
initial size = 1023: moved in memory for size <= 1020
initial size = 1024: moved in memory for size <= 1024
initial size = 1025: moved in memory for size <= 1022
initial size = 1448: moved in memory for size <= 1445
initial size = 2047: moved in memory for size <= 2043
initial size = 2048: moved in memory for size <= 2048
initial size = 2049: moved in memory for size <= 2046
initial size = 2896: moved in memory for size <= 2893
initial size = 4095: moved in memory for size <= 4091
initial size = 4096: moved in memory for size <= 4096
initial size = 4097: moved in memory for size <= 4094
initial size = 5793: moved in memory for size <= 5790
initial size = 8191: moved in memory for size <= 8188
initial size = 8192: moved in memory for size <= 8192
initial size = 8193: moved in memory for size <= 8190
initial size = 11585: moved in memory for size <= 11582
initial size = 16383: moved in memory for size <= 16380
initial size = 16384: moved in memory for size <= 16384
initial size = 16385: moved in memory for size <= 0
initial size = 23170: moved in memory for size <= 0
initial size = 32767: moved in memory for size <= 0
initial size = 32768: moved in memory for size <= 0
initial size = 32769: moved in memory for size <= 0
initial size = 46341: moved in memory for size <= 0
initial size = 65535: moved in memory for size <= 0
initial size = 65536: moved in memory for size <= 0
initial size = 65537: moved in memory for size <= 0
*/
