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Re: [Qemu-devel] [PATCH 2/2] filemon: ensure watch IDs are unique to QFi
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From: |
Daniel P . Berrangé |
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Subject: |
Re: [Qemu-devel] [PATCH 2/2] filemon: ensure watch IDs are unique to QFileMonitor scope |
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Date: |
Fri, 15 Mar 2019 16:54:53 +0000 |
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User-agent: |
Mutt/1.11.3 (2019-02-01) |
On Fri, Mar 15, 2019 at 12:27:06PM -0400, Bandan Das wrote:
> Daniel P. Berrangé <address@hidden> writes:
>
> > The watch IDs are mistakenly only unique within the scope of the
> > directory being monitored. This is not useful for clients which are
> > monitoring multiple directories. They require watch IDs to be unique
> > globally within the QFileMonitor scope.
> >
> > Signed-off-by: Daniel P. Berrangé <address@hidden>
> > ---
> > tests/test-util-filemonitor.c | 116 +++++++++++++++++++++++++++++++---
> > util/filemonitor-inotify.c | 5 +-
> > 2 files changed, 110 insertions(+), 11 deletions(-)
> >
> > diff --git a/tests/test-util-filemonitor.c b/tests/test-util-filemonitor.c
> > index ea3715a8f4..71a7cf5de0 100644
> > --- a/tests/test-util-filemonitor.c
> > +++ b/tests/test-util-filemonitor.c
> > @@ -35,6 +35,8 @@ enum {
> > QFILE_MONITOR_TEST_OP_RENAME,
> > QFILE_MONITOR_TEST_OP_TOUCH,
> > QFILE_MONITOR_TEST_OP_UNLINK,
> > + QFILE_MONITOR_TEST_OP_MKDIR,
> > + QFILE_MONITOR_TEST_OP_RMDIR,
> > };
> >
> > typedef struct {
> > @@ -298,6 +300,54 @@ test_file_monitor_events(void)
> > .eventid = QFILE_MONITOR_EVENT_DELETED },
> >
> >
> > + { .type = QFILE_MONITOR_TEST_OP_MKDIR,
> > + .filesrc = "fish", },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "fish", .watchid = 0,
> > + .eventid = QFILE_MONITOR_EVENT_CREATED },
> > +
> > +
> > + { .type = QFILE_MONITOR_TEST_OP_ADD_WATCH,
> > + .filesrc = "fish/", .watchid = 4 },
> > + { .type = QFILE_MONITOR_TEST_OP_ADD_WATCH,
> > + .filesrc = "fish/one.txt", .watchid = 5 },
> > + { .type = QFILE_MONITOR_TEST_OP_CREATE,
> > + .filesrc = "fish/one.txt", },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "one.txt", .watchid = 4,
> > + .eventid = QFILE_MONITOR_EVENT_CREATED },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "one.txt", .watchid = 5,
> > + .eventid = QFILE_MONITOR_EVENT_CREATED },
> > +
> > +
> > + { .type = QFILE_MONITOR_TEST_OP_DEL_WATCH,
> > + .filesrc = "fish/one.txt", .watchid = 5 },
> > + { .type = QFILE_MONITOR_TEST_OP_RENAME,
> > + .filesrc = "fish/one.txt", .filedst = "two.txt", },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "one.txt", .watchid = 4,
> > + .eventid = QFILE_MONITOR_EVENT_DELETED },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "two.txt", .watchid = 0,
> > + .eventid = QFILE_MONITOR_EVENT_CREATED },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "two.txt", .watchid = 2,
> > + .eventid = QFILE_MONITOR_EVENT_CREATED },
> > +
> > +
> > + { .type = QFILE_MONITOR_TEST_OP_RMDIR,
> > + .filesrc = "fish", },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "", .watchid = 4,
> > + .eventid = QFILE_MONITOR_EVENT_IGNORED },
> > + { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > + .filesrc = "fish", .watchid = 0,
> > + .eventid = QFILE_MONITOR_EVENT_DELETED },
> > + { .type = QFILE_MONITOR_TEST_OP_DEL_WATCH,
> > + .filesrc = "fish", .watchid = 4 },
> > +
> > +
> > { .type = QFILE_MONITOR_TEST_OP_UNLINK,
> > .filesrc = "two.txt", },
> > { .type = QFILE_MONITOR_TEST_OP_EVENT,
> > @@ -366,6 +416,8 @@ test_file_monitor_events(void)
> > int fd;
> > int watchid;
> > struct utimbuf ubuf;
> > + char *watchdir;
> > + const char *watchfile;
> >
> > pathsrc = g_strdup_printf("%s/%s", dir, op->filesrc);
> > if (op->filedst) {
> > @@ -378,13 +430,26 @@ test_file_monitor_events(void)
> > g_printerr("Add watch %s %s %d\n",
> > dir, op->filesrc, op->watchid);
> > }
> > + if (op->filesrc && strchr(op->filesrc, '/')) {
> > + watchdir = g_strdup_printf("%s/%s", dir, op->filesrc);
> > + watchfile = strrchr(watchdir, '/');
> > + *(char *)watchfile = '\0';
> > + watchfile++;
> > + if (*watchfile == '\0') {
> > + watchfile = NULL;
> > + }
> > + } else {
> > + watchdir = g_strdup(dir);
> > + watchfile = op->filesrc;
> > + }
> > watchid =
> > qemu_file_monitor_add_watch(mon,
> > - dir,
> > - op->filesrc,
> > + watchdir,
> > + watchfile,
> > qemu_file_monitor_test_handler,
> > &data,
> > &local_err);
> > + g_free(watchdir);
> > if (watchid < 0) {
> > g_printerr("Unable to add watch %s",
> > error_get_pretty(local_err));
> > @@ -400,9 +465,17 @@ test_file_monitor_events(void)
> > if (debug) {
> > g_printerr("Del watch %s %d\n", dir, op->watchid);
> > }
> > + if (op->filesrc && strchr(op->filesrc, '/')) {
> > + watchdir = g_strdup_printf("%s/%s", dir, op->filesrc);
> > + watchfile = strrchr(watchdir, '/');
> > + *(char *)watchfile = '\0';
> > + } else {
> > + watchdir = g_strdup(dir);
> > + }
> > qemu_file_monitor_remove_watch(mon,
> > - dir,
> > + watchdir,
> > op->watchid);
> > + g_free(watchdir);
> > break;
> > case QFILE_MONITOR_TEST_OP_EVENT:
> > if (debug) {
> > @@ -492,6 +565,28 @@ test_file_monitor_events(void)
> > }
> > break;
> >
> > + case QFILE_MONITOR_TEST_OP_MKDIR:
> > + if (debug) {
> > + g_printerr("Mkdir %s\n", pathsrc);
> > + }
> > + if (mkdir(pathsrc, 0700) < 0) {
> > + g_printerr("Unable to mkdir %s: %s",
> > + pathsrc, strerror(errno));
> > + goto cleanup;
> > + }
> > + break;
> > +
> > + case QFILE_MONITOR_TEST_OP_RMDIR:
> > + if (debug) {
> > + g_printerr("Rmdir %s\n", pathsrc);
> > + }
> > + if (rmdir(pathsrc) < 0) {
> > + g_printerr("Unable to rmdir %s: %s",
> > + pathsrc, strerror(errno));
> > + goto cleanup;
> > + }
> > + break;
> > +
> > default:
> > g_assert_not_reached();
> > }
> > @@ -532,13 +627,18 @@ test_file_monitor_events(void)
> > const QFileMonitorTestOp *op = &(ops[i]);
> > char *path = g_strdup_printf("%s/%s",
> > dir, op->filesrc);
> > - unlink(path);
> > - g_free(path);
> > - if (op->filedst) {
> > - path = g_strdup_printf("%s/%s",
> > - dir, op->filedst);
> > + if (op->type == QFILE_MONITOR_TEST_OP_MKDIR) {
> > + rmdir(path);
> > + g_free(path);
> > + } else {
> > unlink(path);
> > g_free(path);
> > + if (op->filedst) {
> > + path = g_strdup_printf("%s/%s",
> > + dir, op->filedst);
> > + unlink(path);
> > + g_free(path);
> > + }
> > }
> > }
> > if (rmdir(dir) < 0) {
> > diff --git a/util/filemonitor-inotify.c b/util/filemonitor-inotify.c
> > index 3a72be037f..3eb29f860b 100644
> > --- a/util/filemonitor-inotify.c
> > +++ b/util/filemonitor-inotify.c
> > @@ -29,7 +29,7 @@
> >
> > struct QFileMonitor {
> > int fd;
> > -
> > + int nextid; /* watch ID counter */
> > QemuMutex lock; /* protects dirs & idmap */
> > GHashTable *dirs; /* dirname => QFileMonitorDir */
> > GHashTable *idmap; /* inotify ID => dirname */
> > @@ -47,7 +47,6 @@ typedef struct {
> > typedef struct {
> > char *path;
> > int id; /* inotify ID */
> > - int nextid; /* watch ID counter */
> > GArray *watches; /* QFileMonitorWatch elements */
> > } QFileMonitorDir;
> >
> > @@ -277,7 +276,7 @@ qemu_file_monitor_add_watch(QFileMonitor *mon,
> > }
> > }
> >
> > - watch.id = dir->nextid++;
> > + watch.id = mon->nextid++;
> > watch.filename = g_strdup(filename);
> > watch.cb = cb;
> > watch.opaque = opaque;
>
> Thanks, this fixes it! I had a related question about the way
> qemu_file_monitor_add_watch works.
>
> Am I correct in understanding that if there is already a watch on a dir,
> we return back mon->nextid++ i.e the next free id. Why don't we return
> back the originally assigned watchid ?
inotify watches are a per-directory scope thing, but this API is aiming
to present the ability to have per-file scope watches as it is more
convenient to have those semantics for some users in QEMU. Thus many
QEMU level watches are mapped to the same low level inotify watch.
The watch ID is used to unregister a watch later, and while I could have
done ref counting against a common watch ID, I find it clearer to maintain
separate watch IDs for every thing the caller watches. If nothing else it
makes the debugging easier as you can see the relation between events
received and the original watch registration.
Regards,
Daniel
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