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shred: enable direct I/O when possible

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Commit v5.92-1057-g43d487b introduced a regression
in coreutils 6.0 where it removed the page alignment
of the buffer to write, thus disabling direct I/O.
We want to use direct I/O when possible to avoid
impacting the page cache at least, as we know we don't
want to cache the data we're writing.

* src/shred.c (dopass): Allocate the buffer on the heap,
while using a more general calculation to allow to have
the output size independent from the fillpattern() size
constraint of a multiple of 3.  Also we dispense with the
union as it's no longer needed given we're aligning on
a page boundary and thus don't need to explicitly handle
uint32_t alignment.
This commit is contained in:
Pádraig Brady
2013-11-04 23:14:10 +00:00
parent d60e04424d
commit ebaf961f3a
2 changed files with 39 additions and 24 deletions
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NEWS
+3
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@@ -87,6 +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]
split --line-bytes=SIZE, now only allocates memory as needed rather
than allocating SIZE bytes at program start.
src/shred.c
+36 -24
View File
@@ -359,19 +359,18 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
size_t soff; /* Offset into buffer for next write */
ssize_t ssize; /* Return value from write */
/* Fill pattern buffer. Aligning it to a 32-bit boundary speeds up randread
in some cases. */
typedef uint32_t fill_pattern_buffer[3 * 1024];
union
{
fill_pattern_buffer buffer;
char c[sizeof (fill_pattern_buffer)];
unsigned char u[sizeof (fill_pattern_buffer)];
} r;
/* 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 PAGE_ALIGN_SLOP (page_size - 1) /* So directio works */
#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);
off_t sizeof_r = sizeof r;
char pass_string[PASS_NAME_SIZE]; /* Name of current pass */
bool write_error = false;
bool other_error = false;
bool first_write = true;
/* Printable previous offset into the file */
@@ -381,15 +380,16 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
if (lseek (fd, 0, SEEK_SET) == -1)
{
error (0, errno, _("%s: cannot rewind"), qname);
return -1;
other_error = true;
goto free_pattern_mem;
}
/* Constant fill patterns need only be set up once. */
if (type >= 0)
{
lim = (0 <= size && size < sizeof_r ? size : sizeof_r);
fillpattern (type, r.u, lim);
passname (r.u, pass_string);
lim = (0 <= size && size < FILLPATTERN_SIZE ? size : FILLPATTERN_SIZE);
fillpattern (type, pbuf, lim);
passname (pbuf, pass_string);
}
else
{
@@ -408,8 +408,8 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
while (true)
{
/* How much to write this time? */
lim = sizeof r;
if (0 <= size && size - offset < sizeof_r)
lim = OUTPUT_SIZE;
if (0 <= size && size - offset < OUTPUT_SIZE)
{
if (size < offset)
break;
@@ -418,11 +418,11 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
break;
}
if (type < 0)
randread (s, &r, lim);
randread (s, pbuf, lim);
/* Loop to retry partial writes. */
for (soff = 0; soff < lim; soff += ssize, first_write = false)
{
ssize = write (fd, r.c + soff, lim - soff);
ssize = write (fd, pbuf + soff, lim - soff);
if (ssize <= 0)
{
if (size < 0 && (ssize == 0 || errno == ENOSPC))
@@ -456,7 +456,7 @@ 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 (sizeof r % SECTOR_SIZE == 0);
verify (OUTPUT_SIZE % SECTOR_SIZE == 0);
if (errnum == EIO && 0 <= size && (soff | SECTOR_MASK) < lim)
{
size_t soff1 = (soff | SECTOR_MASK) + 1;
@@ -469,7 +469,8 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
}
error (0, errno, _("%s: lseek failed"), qname);
}
return -1;
other_error = true;
goto free_pattern_mem;
}
}
}
@@ -479,7 +480,8 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
if (offset > OFF_T_MAX - (off_t) soff)
{
error (0, 0, _("%s: file too large"), qname);
return -1;
other_error = true;
goto free_pattern_mem;
}
offset += soff;
@@ -536,7 +538,10 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
if (dosync (fd, qname) != 0)
{
if (errno != EIO)
return -1;
{
other_error = true;
goto free_pattern_mem;
}
write_error = true;
}
}
@@ -547,11 +552,18 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
if (dosync (fd, qname) != 0)
{
if (errno != EIO)
return -1;
{
other_error = true;
goto free_pattern_mem;
}
write_error = true;
}
return write_error;
free_pattern_mem:
memset (pbuf, 0, FILLPATTERN_SIZE);
free (fill_pattern_mem);
return other_error ? -1 : write_error;
}
/*