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virfile: safezero: align mmap offset to page size

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mmap's offset must be aligned to page size or mapping will fail.
mmap-based safezero is only used if posix_fallocate isn't available.

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
This commit is contained in:
Oskari Saarenmaa 2013-09-30 14:01:45 +03:00 committed by Michal Privoznik
parent 11d9dd7ba0
commit edc61bf63e
1 changed files with 11 additions and 3 deletions
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14
src/util/virfile.c
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@ -1038,9 +1038,16 @@ safezero(int fd, off_t offset, off_t len)
int int
safezero(int fd, off_t offset, off_t len) safezero(int fd, off_t offset, off_t len)
{ {
static long pagemask = 0;
off_t map_skip;
int r; int r;
char *buf; char *buf;
/* align offset and length, rounding offset down and length up */
if (pagemask == 0)
pagemask = ~(sysconf(_SC_PAGESIZE) - 1);
map_skip = offset - (offset & pagemask);
/* memset wants the mmap'ed file to be present on disk so create a /* memset wants the mmap'ed file to be present on disk so create a
* sparse file * sparse file
*/ */
@ -1048,12 +1055,13 @@ safezero(int fd, off_t offset, off_t len)
if (r < 0) if (r < 0)
return -1; return -1;
buf = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset); buf = mmap(NULL, len + map_skip, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, offset - map_skip);
if (buf == MAP_FAILED) if (buf == MAP_FAILED)
return -1; return -1;
memset(buf, 0, len); memset(buf + map_skip, 0, len);
munmap(buf, len); munmap(buf, len + map_skip);
return 0; return 0;
} }