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block/file-posix: add x-check-page-cache=on|off option

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mincore(2) checks whether pages are resident.  Use it to verify that
page cache has been dropped.

You can trigger a verification failure by mmapping the image file from
another process that loads a byte from a page, forcing it to become
resident.  bdrv_co_invalidate_cache() will fail while that process is
alive.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20180427162312.18583-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2018-04-27 17:23:12 +01:00
parent dd577a26ff
commit 31be8a2a97
2 changed files with 104 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

100
block/file-posix.c
View File

@ -161,6 +161,7 @@ typedef struct BDRVRawState {
bool page_cache_inconsistent:1;
bool has_fallocate;
bool needs_alignment;
bool check_cache_dropped;
PRManager *pr_mgr;
} BDRVRawState;
@ -168,6 +169,7 @@ typedef struct BDRVRawState {
typedef struct BDRVRawReopenState {
int fd;
int open_flags;
bool check_cache_dropped;
} BDRVRawReopenState;
static int fd_open(BlockDriverState *bs);
@ -415,6 +417,11 @@ static QemuOptsList raw_runtime_opts = {
.type = QEMU_OPT_STRING,
.help = "id of persistent reservation manager object (default: none)",
},
{
.name = "x-check-cache-dropped",
.type = QEMU_OPT_BOOL,
.help = "check that page cache was dropped on live migration (default: off)"
},
{ /* end of list */ }
},
};
@ -500,6 +507,9 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
}
}
s->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
false);
s->open_flags = open_flags;
raw_parse_flags(bdrv_flags, &s->open_flags);
@ -777,6 +787,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
{
BDRVRawState *s;
BDRVRawReopenState *rs;
QemuOpts *opts;
int ret = 0;
Error *local_err = NULL;
@ -787,6 +798,19 @@ static int raw_reopen_prepare(BDRVReopenState *state,
state->opaque = g_new0(BDRVRawReopenState, 1);
rs = state->opaque;
rs->fd = -1;
/* Handle options changes */
opts = qemu_opts_create(&raw_runtime_opts, NULL, 0, &error_abort);
qemu_opts_absorb_qdict(opts, state->options, &local_err);
if (local_err) {
error_propagate(errp, local_err);
ret = -EINVAL;
goto out;
}
rs->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
s->check_cache_dropped);
if (s->type == FTYPE_CD) {
rs->open_flags |= O_NONBLOCK;
@ -794,8 +818,6 @@ static int raw_reopen_prepare(BDRVReopenState *state,
raw_parse_flags(state->flags, &rs->open_flags);
rs->fd = -1;
int fcntl_flags = O_APPEND | O_NONBLOCK;
#ifdef O_NOATIME
fcntl_flags |= O_NOATIME;
@ -850,6 +872,8 @@ static int raw_reopen_prepare(BDRVReopenState *state,
}
}
out:
qemu_opts_del(opts);
return ret;
}
@ -858,6 +882,7 @@ static void raw_reopen_commit(BDRVReopenState *state)
BDRVRawReopenState *rs = state->opaque;
BDRVRawState *s = state->bs->opaque;
s->check_cache_dropped = rs->check_cache_dropped;
s->open_flags = rs->open_flags;
qemu_close(s->fd);
@ -2236,6 +2261,73 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs,
return ret | BDRV_BLOCK_OFFSET_VALID;
}
#if defined(__linux__)
/* Verify that the file is not in the page cache */
static void check_cache_dropped(BlockDriverState *bs, Error **errp)
{
const size_t window_size = 128 * 1024 * 1024;
BDRVRawState *s = bs->opaque;
void *window = NULL;
size_t length = 0;
unsigned char *vec;
size_t page_size;
off_t offset;
off_t end;
/* mincore(2) page status information requires 1 byte per page */
page_size = sysconf(_SC_PAGESIZE);
vec = g_malloc(DIV_ROUND_UP(window_size, page_size));
end = raw_getlength(bs);
for (offset = 0; offset < end; offset += window_size) {
void *new_window;
size_t new_length;
size_t vec_end;
size_t i;
int ret;
/* Unmap previous window if size has changed */
new_length = MIN(end - offset, window_size);
if (new_length != length) {
munmap(window, length);
window = NULL;
length = 0;
}
new_window = mmap(window, new_length, PROT_NONE, MAP_PRIVATE,
s->fd, offset);
if (new_window == MAP_FAILED) {
error_setg_errno(errp, errno, "mmap failed");
break;
}
window = new_window;
length = new_length;
ret = mincore(window, length, vec);
if (ret < 0) {
error_setg_errno(errp, errno, "mincore failed");
break;
}
vec_end = DIV_ROUND_UP(length, page_size);
for (i = 0; i < vec_end; i++) {
if (vec[i] & 0x1) {
error_setg(errp, "page cache still in use!");
break;
}
}
}
if (window) {
munmap(window, length);
}
g_free(vec);
}
#endif /* __linux__ */
static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs,
Error **errp)
{
@ -2269,6 +2361,10 @@ static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs,
error_setg_errno(errp, ret, "fadvise failed");
return;
}
if (s->check_cache_dropped) {
check_cache_dropped(bs, errp);
}
#else /* __linux__ */
/* Do nothing. Live migration to a remote host with cache.direct=off is
* unsupported on other host operating systems. Cache consistency issues

7
qapi/block-core.json
View File

@ -2530,6 +2530,10 @@
# @locking: whether to enable file locking. If set to 'auto', only enable
# when Open File Descriptor (OFD) locking API is available
# (default: auto, since 2.10)
# @x-check-cache-dropped: whether to check that page cache was dropped on live
# migration. May cause noticeable delays if the image
# file is large, do not use in production.
# (default: off) (since: 2.13)
#
# Since: 2.9
##
@ -2537,7 +2541,8 @@
'data': { 'filename': 'str',
'*pr-manager': 'str',
'*locking': 'OnOffAuto',
'*aio': 'BlockdevAioOptions' } }
'*aio': 'BlockdevAioOptions',
'*x-check-cache-dropped': 'bool' } }
##
# @BlockdevOptionsNull: