[libvirt] [PATCH] virfile: safezero: fall back to writing block by block if mmap fails
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> --- src/util/virfile.c | 34 ++++++++++++++-------------------- 1 file changed, 14 insertions(+), 20 deletions(-) diff --git a/src/util/virfile.c b/src/util/virfile.c index 16f8101..f662127 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -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; -} - -# else /* HAVE_MMAP */ + return 0; + } -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 */ -- 1.8.3.1
On 02.10.2013 09:31, Oskari Saarenmaa wrote:
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> --- src/util/virfile.c | 34 ++++++++++++++-------------------- 1 file changed, 14 insertions(+), 20 deletions(-)
ACKed and pushed. Thanks for your contribution! Michal
My previous commit 7dc1d4ab was supposed to change safezero to allocate 1 megabyte at maximum, but had the logic reversed and will allocate 1 megabyte at minimum (and a lot more at maximum.) Signed-off-by: Oskari Saarenmaa <os@ohmu.fi> --- src/util/virfile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/util/virfile.c b/src/util/virfile.c index f662127..e10de5a 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -1075,7 +1075,7 @@ safezero(int fd, off_t offset, off_t len) /* Split up the write in small chunks so as not to allocate lots of RAM */ remain = len; - bytes = MAX(1024 * 1024, len); + bytes = MIN(1024 * 1024, len); r = VIR_ALLOC_N(buf, bytes); if (r < 0) { -- 1.8.3.1
On 04.10.2013 15:49, Oskari Saarenmaa wrote:
My previous commit 7dc1d4ab was supposed to change safezero to allocate 1 megabyte at maximum, but had the logic reversed and will allocate 1 megabyte at minimum (and a lot more at maximum.)
Signed-off-by: Oskari Saarenmaa <os@ohmu.fi> --- src/util/virfile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/util/virfile.c b/src/util/virfile.c index f662127..e10de5a 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -1075,7 +1075,7 @@ safezero(int fd, off_t offset, off_t len)
/* Split up the write in small chunks so as not to allocate lots of RAM */ remain = len; - bytes = MAX(1024 * 1024, len); + bytes = MIN(1024 * 1024, len);
r = VIR_ALLOC_N(buf, bytes); if (r < 0) {
Ooops. ACKed and pushed. Meanwhile I'm gonna hide someplace to be alone with shame :) Michal
participants (2)
-
Michal Privoznik -
Oskari Saarenmaa