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 <fen...@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 -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|