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virfile: safezero: fall back to writing block by block if mmap fails

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mmap can fail on 32-bit systems if we're trying to zero out a lot of data.
Fall back to using block-by-block writing in that case.  While we could map
smaller blocks it's unlikely that this code is used a lot and its easier to
just fall back to one of the existing methods.

Also modified the block-by-block zeroing to not allocate a megabyte of
zeroes if we're writing less than that.

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
This commit is contained in:
Oskari Saarenmaa 2013-10-02 10:31:09 +03:00 committed by Michal Privoznik
parent 68cc45b6f9
commit 7dc1d4ab89
1 changed files with 14 additions and 20 deletions
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34
src/util/virfile.c
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@ -1032,16 +1032,18 @@ safezero(int fd, off_t offset, off_t len)
errno = ret;
return -1;
}
#else
# ifdef HAVE_MMAP
int
safezero(int fd, off_t offset, off_t len)
{
static long pagemask = 0;
off_t map_skip;
int r;
char *buf;
unsigned long long remain, bytes;
# ifdef HAVE_MMAP
static long pagemask = 0;
off_t map_skip;
/* align offset and length, rounding offset down and length up */
if (pagemask == 0)
@ -1057,30 +1059,23 @@ safezero(int fd, off_t offset, off_t len)
buf = mmap(NULL, len + map_skip, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, offset - map_skip);
if (buf == MAP_FAILED)
return -1;
if (buf != MAP_FAILED) {
memset(buf + map_skip, 0, len);
munmap(buf, len + map_skip);
memset(buf + map_skip, 0, len);
munmap(buf, len + map_skip);
return 0;
}
return 0;
}
# else /* HAVE_MMAP */
int
safezero(int fd, off_t offset, off_t len)
{
int r;
char *buf;
unsigned long long remain, bytes;
/* fall back to writing zeroes using safewrite if mmap fails (for
* example because of virtual memory limits) */
# endif /* HAVE_MMAP */
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
/* Split up the write in small chunks so as not to allocate lots of RAM */
remain = len;
bytes = 1024 * 1024;
bytes = MAX(1024 * 1024, len);
r = VIR_ALLOC_N(buf, bytes);
if (r < 0) {
@ -1104,7 +1099,6 @@ safezero(int fd, off_t offset, off_t len)
VIR_FREE(buf);
return 0;
}
# endif /* HAVE_MMAP */
#endif /* HAVE_POSIX_FALLOCATE */