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shred: write larger chunks when possible

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* src/shred.c (dopass): When not needing to write periodic patterns,
use a 64KiB block size to reduce the number of write system calls.
This commit is contained in:
Pádraig Brady
2013-11-04 23:14:11 +00:00
parent ebaf961f3a
commit 2c6736f92f
2 changed files with 32 additions and 7 deletions
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NEWS
+3 -2
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@@ -87,8 +87,9 @@ GNU coreutils NEWS -*- outline -*-
Reservoir sampling is used to limit memory usage based on the number of
outputs, rather than the number of inputs.
shred once again uses direct I/O where available.
[Regression introduced in coreutils-6.0]
shred once again uses direct I/O where available, and increases write block
size from 12KiB to 64KiB when possible.
[Direct I/O regression introduced in coreutils-6.0]
split --line-bytes=SIZE, now only allocates memory as needed rather
than allocating SIZE bytes at program start.
src/shred.c
+29 -5
View File
@@ -222,6 +222,25 @@ to be recovered later.\n\
exit (status);
}
/*
* Determine if pattern type is periodic or not.
*/
static bool
periodic_pattern (int type)
{
if (type <= 0)
return false;
unsigned char r[3];
unsigned int bits = type & 0xfff;
bits |= bits << 12;
r[0] = (bits >> 4) & 255;
r[1] = (bits >> 8) & 255;
r[2] = bits & 255;
return (r[0] != r[1]) || (r[0] != r[2]);
}
/*
* Fill a buffer with a fixed pattern.
@@ -361,9 +380,13 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
/* Fill pattern buffer. Aligning it to a page so we can do direct I/O. */
size_t page_size = getpagesize ();
#define OUTPUT_SIZE (12 * 1024)
#define PERIODIC_OUTPUT_SIZE (12 * 1024)
#define NONPERIODIC_OUTPUT_SIZE (64 * 1024)
verify (PERIODIC_OUTPUT_SIZE % 3 == 0);
size_t output_size = periodic_pattern (type)
? PERIODIC_OUTPUT_SIZE : NONPERIODIC_OUTPUT_SIZE;
#define PAGE_ALIGN_SLOP (page_size - 1) /* So directio works */
#define FILLPATTERN_SIZE (((OUTPUT_SIZE + 2) / 3) * 3) /* Multiple of 3 */
#define FILLPATTERN_SIZE (((output_size + 2) / 3) * 3) /* Multiple of 3 */
#define PATTERNBUF_SIZE (PAGE_ALIGN_SLOP + FILLPATTERN_SIZE)
void *fill_pattern_mem = xmalloc (PATTERNBUF_SIZE);
unsigned char *pbuf = ptr_align (fill_pattern_mem, page_size);
@@ -408,8 +431,8 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
while (true)
{
/* How much to write this time? */
lim = OUTPUT_SIZE;
if (0 <= size && size - offset < OUTPUT_SIZE)
lim = output_size;
if (0 <= size && size - offset < output_size)
{
if (size < offset)
break;
@@ -456,7 +479,8 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
out. Thus, it shouldn't give up on bad blocks. This
code works because lim is always a multiple of
SECTOR_SIZE, except at the end. */
verify (OUTPUT_SIZE % SECTOR_SIZE == 0);
verify (PERIODIC_OUTPUT_SIZE % SECTOR_SIZE == 0);
verify (NONPERIODIC_OUTPUT_SIZE % SECTOR_SIZE == 0);
if (errnum == EIO && 0 <= size && (soff | SECTOR_MASK) < lim)
{
size_t soff1 = (soff | SECTOR_MASK) + 1;