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Re: [PATCH] file-posix: detect the lock using the real file
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH] file-posix: detect the lock using the real file |
Date: |
Tue, 8 Dec 2020 13:45:19 +0000 |
User-agent: |
Mutt/1.14.6 (2020-07-11) |
On Tue, Dec 08, 2020 at 08:59:37PM +0800, Li Feng wrote:
> This patch addresses this issue:
> When accessing a volume on an NFS filesystem without supporting the file lock,
> tools, like qemu-img, will complain "Failed to lock byte 100".
>
> In the original code, the qemu_has_ofd_lock will test the lock on the
> "/dev/null" pseudo-file. Actually, the file.locking is per-drive property,
> which depends on the underlay filesystem.
IIUC, the problem you're describing is one of whether the filesystem
supports fcntl locking at all, which is indeed a per-FS check.
The QEMU code being changed though is just about detecting whether
the host OS supports OFD to not, which is supposed to be a kernel
level feature applied universally to all FS types.
>
> In this patch, make the 'qemu_has_ofd_lock' with a filename be more generic
> and reasonable.
>
> Signed-off-by: Li Feng <fengli@smartx.com>
> ---
> block/file-posix.c | 32 +++++++++++++++-------------
> include/qemu/osdep.h | 2 +-
> tests/test-image-locking.c | 2 +-
> util/osdep.c | 43 ++++++++++++++++++++++++--------------
> 4 files changed, 47 insertions(+), 32 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 806764f7e3..03be1b188c 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -595,7 +595,7 @@ static int raw_open_common(BlockDriverState *bs, QDict
> *options,
> switch (locking) {
> case ON_OFF_AUTO_ON:
> s->use_lock = true;
> - if (!qemu_has_ofd_lock()) {
> + if (!qemu_has_ofd_lock(filename)) {
> warn_report("File lock requested but OFD locking syscall is "
> "unavailable, falling back to POSIX file locks");
> error_printf("Due to the implementation, locks can be lost "
> @@ -606,7 +606,7 @@ static int raw_open_common(BlockDriverState *bs, QDict
> *options,
> s->use_lock = false;
> break;
> case ON_OFF_AUTO_AUTO:
> - s->use_lock = qemu_has_ofd_lock();
> + s->use_lock = qemu_has_ofd_lock(filename);
> break;
> default:
> abort();
> @@ -2388,6 +2388,7 @@ raw_co_create(BlockdevCreateOptions *options, Error
> **errp)
> int fd;
> uint64_t perm, shared;
> int result = 0;
> + bool use_lock;
>
> /* Validate options and set default values */
> assert(options->driver == BLOCKDEV_DRIVER_FILE);
> @@ -2428,19 +2429,22 @@ raw_co_create(BlockdevCreateOptions *options, Error
> **errp)
> perm = BLK_PERM_WRITE | BLK_PERM_RESIZE;
> shared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
>
> - /* Step one: Take locks */
> - result = raw_apply_lock_bytes(NULL, fd, perm, ~shared, false, errp);
> - if (result < 0) {
> - goto out_close;
> - }
> + use_lock = qemu_has_ofd_lock(file_opts->filename);
> + if (use_lock) {
> + /* Step one: Take locks */
> + result = raw_apply_lock_bytes(NULL, fd, perm, ~shared, false, errp);
> + if (result < 0) {
> + goto out_close;
> + }
>
> - /* Step two: Check that nobody else has taken conflicting locks */
> - result = raw_check_lock_bytes(fd, perm, shared, errp);
> - if (result < 0) {
> - error_append_hint(errp,
> - "Is another process using the image [%s]?\n",
> - file_opts->filename);
> - goto out_unlock;
> + /* Step two: Check that nobody else has taken conflicting locks */
> + result = raw_check_lock_bytes(fd, perm, shared, errp);
> + if (result < 0) {
> + error_append_hint(errp,
> + "Is another process using the image [%s]?\n",
> + file_opts->filename);
> + goto out_unlock;
> + }
> }
>
> /* Clear the file by truncating it to 0 */
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index f9ec8c84e9..349adad465 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -512,7 +512,7 @@ int qemu_dup(int fd);
> int qemu_lock_fd(int fd, int64_t start, int64_t len, bool exclusive);
> int qemu_unlock_fd(int fd, int64_t start, int64_t len);
> int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive);
> -bool qemu_has_ofd_lock(void);
> +bool qemu_has_ofd_lock(const char *filename);
> #endif
>
> #if defined(__HAIKU__) && defined(__i386__)
> diff --git a/tests/test-image-locking.c b/tests/test-image-locking.c
> index ba057bd66c..3e80246081 100644
> --- a/tests/test-image-locking.c
> +++ b/tests/test-image-locking.c
> @@ -149,7 +149,7 @@ int main(int argc, char **argv)
>
> g_test_init(&argc, &argv, NULL);
>
> - if (qemu_has_ofd_lock()) {
> + if (qemu_has_ofd_lock(NULL)) {
> g_test_add_func("/image-locking/basic", test_image_locking_basic);
> g_test_add_func("/image-locking/set-perm-abort",
> test_set_perm_abort);
> }
> diff --git a/util/osdep.c b/util/osdep.c
> index 66d01b9160..e7e502edd1 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -42,6 +42,7 @@ extern int madvise(char *, size_t, int);
> static bool fips_enabled = false;
>
> static const char *hw_version = QEMU_HW_VERSION;
> +static const char *null_device = "/dev/null";
>
> int socket_set_cork(int fd, int v)
> {
> @@ -187,11 +188,10 @@ static int qemu_parse_fdset(const char *param)
> return qemu_parse_fd(param);
> }
>
> -static void qemu_probe_lock_ops(void)
> +static void qemu_probe_lock_ops_fd(int fd)
> {
> if (fcntl_op_setlk == -1) {
> #ifdef F_OFD_SETLK
> - int fd;
> int ret;
> struct flock fl = {
> .l_whence = SEEK_SET,
> @@ -200,17 +200,7 @@ static void qemu_probe_lock_ops(void)
> .l_type = F_WRLCK,
> };
>
> - fd = open("/dev/null", O_RDWR);
> - if (fd < 0) {
> - fprintf(stderr,
> - "Failed to open /dev/null for OFD lock probing: %s\n",
> - strerror(errno));
> - fcntl_op_setlk = F_SETLK;
> - fcntl_op_getlk = F_GETLK;
> - return;
> - }
> ret = fcntl(fd, F_OFD_GETLK, &fl);
> - close(fd);
> if (!ret) {
> fcntl_op_setlk = F_OFD_SETLK;
> fcntl_op_getlk = F_OFD_GETLK;
> @@ -225,9 +215,30 @@ static void qemu_probe_lock_ops(void)
> }
> }
>
> -bool qemu_has_ofd_lock(void)
> +static void qemu_probe_lock_ops(const char *filename)
> +{
> + int fd;
> + if (filename) {
> + fd = open(filename, O_RDWR);
> + } else {
> + fd = open(null_device, O_RDONLY);
> + }
> + if (fd < 0) {
> + fprintf(stderr,
> + "Failed to open %s for OFD lock probing: %s\n",
> + filename ? filename : null_device,
> + strerror(errno));
> + fcntl_op_setlk = F_SETLK;
> + fcntl_op_getlk = F_GETLK;
> + return;
> + }
> + qemu_probe_lock_ops_fd(fd);
> + close(fd);
> +}
> +
This method now does a test whose results will vary based on the
filename passed in, but it is updating a global variable to say
whether to use OFD locks. This is looks badly broken when using
files across different filesystems.
IMHO the raw_co_create method just needs to use a dedicated method
to check whether fcntl locks are supposed, and all this broken
refactoring of the OFD check should be removed.
> +bool qemu_has_ofd_lock(const char *filename)
> {
> - qemu_probe_lock_ops();
> + qemu_probe_lock_ops(filename);
> #ifdef F_OFD_SETLK
> return fcntl_op_setlk == F_OFD_SETLK;
> #else
> @@ -244,7 +255,7 @@ static int qemu_lock_fcntl(int fd, int64_t start, int64_t
> len, int fl_type)
> .l_len = len,
> .l_type = fl_type,
> };
> - qemu_probe_lock_ops();
> + qemu_probe_lock_ops_fd(fd);
> do {
> ret = fcntl(fd, fcntl_op_setlk, &fl);
> } while (ret == -1 && errno == EINTR);
> @@ -270,7 +281,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len,
> bool exclusive)
> .l_len = len,
> .l_type = exclusive ? F_WRLCK : F_RDLCK,
> };
> - qemu_probe_lock_ops();
> + qemu_probe_lock_ops_fd(fd);
> ret = fcntl(fd, fcntl_op_getlk, &fl);
> if (ret == -1) {
> return -errno;
> --
> 2.24.3
>
>
Regards,
Daniel
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- [PATCH] file-posix: detect the lock using the real file, Li Feng, 2020/12/08
- Re: [PATCH] file-posix: detect the lock using the real file,
Daniel P . Berrangé <=
- Re: [PATCH] file-posix: detect the lock using the real file, Kevin Wolf, 2020/12/08
- Re: [PATCH] file-posix: detect the lock using the real file, Li Feng, 2020/12/08
- Re: [PATCH] file-posix: detect the lock using the real file, Daniel P . Berrangé, 2020/12/09
- Re: [PATCH] file-posix: detect the lock using the real file, Kevin Wolf, 2020/12/09
- Re: [PATCH] file-posix: detect the lock using the real file, Li Feng, 2020/12/10
- Re: [PATCH] file-posix: detect the lock using the real file, Daniel P . Berrangé, 2020/12/10
- Re: [PATCH] file-posix: detect the lock using the real file, Feng Li, 2020/12/10
- Re: [PATCH] file-posix: detect the lock using the real file, Daniel P . Berrangé, 2020/12/10
[PATCH v2] file-posix: detect the lock using the real file, Li Feng, 2020/12/08