On Wed 09-09-20 19:03:07, Amir Goldstein wrote: > On Wed, Sep 9, 2020 at 2:11 PM Jan Kara <jack@xxxxxxx> wrote: > > > > On Wed 09-09-20 10:36:57, Amir Goldstein wrote: > > > On Wed, Sep 9, 2020 at 10:00 AM Xiaoming Ni <nixiaoming@xxxxxxxxxx> wrote: > > > > > > > > On 2020/9/9 11:44, Amir Goldstein wrote: > > > > > On Tue, Sep 8, 2020 at 8:19 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > >> > > > > >> On Tue, Sep 08, 2020 at 04:18:29PM +0300, Amir Goldstein wrote: > > > > >>> On Tue, Sep 8, 2020 at 3:53 PM Xiaoming Ni <nixiaoming@xxxxxxxxxx> wrote: > > > > >>>> For example, in fs/coredump.c, do_coredump() calls filp_open() to > > > > >>>> generate core files. > > > > >>>> In this scenario, the fsnotify_open() notification is missing. > > > > >>> > > > > >>> I am not convinced that we should generate an event. > > > > >>> You will have to explain in what is the real world use case that requires this > > > > >>> event to be generated. > > > > >> > > > > >> Take the typical usage for fsnotify of a graphical file manager. > > > > >> It would be nice if the file manager showed a corefile as soon as it > > > > >> appeared in a directory rather than waiting until some other operation > > > > >> in that directory caused those directory contents to be refreshed. > > > > > > > > > > fsnotify_open() is not the correct notification for file managers IMO. > > > > > fsnotify_create() is and it will be called in this case. > > > > > > > > > > If the reason you are interested in open events is because you want > > > > > to monitor the entire filesystem then welcome to the future - > > > > > FAN_CREATE is supported since kernel v5.1. > > > > > > > > > > Is there another real life case you have in mind where you think users > > > > > should be able to get an open fd for a file that the kernel has opened? > > > > > Because that is what FAN_OPEN will do. > > > > > > > > > > > > > There are also cases where file is opened in read-only mode using > > > > filp_open(). > > > > > > > > case1: nfsd4_init_recdir() call filp_open() > > > > filp_open() > > > > nfsd4_init_recdir() fs/nfsd/nfs4recover.c#L543 > > > > > > > > L70: static char user_recovery_dirname[PATH_MAX] = > > > > "/var/lib/nfs/v4recovery"; > > > > L543: nn->rec_file = filp_open(user_recovery_dirname, O_RDONLY | > > > > O_DIRECTORY, 0); > > > > > > > > > > > > case2: ima_read_policy() > > > > filp_open() > > > > kernel_read_file_from_path() fs/exec.c#L1004 > > > > ima_read_policy() security/integrity/ima/ima_fs.c#L286 > > > > ima_write_policy() security/integrity/ima/ima_fs.c#L335 > > > > ima_measure_policy_ops security/integrity/ima/ima_fs.c#L443 > > > > sys_write() > > > > > > > > case3: use do_file_open_root() to open file > > > > do_file_open_root() > > > > file_open_root() fs/open.c#L1159 > > > > kernel_read_file_from_path_initns() fs/exec.c#L1029 > > > > fw_get_filesystem_firmware() drivers/base/firmware_loader/main.c#L498 > > > > > > > > Do we need to add fsnotify_open() in these scenarios? > > > > > > We do not *need* to add fsnotify_open() if there is no concrete use case > > > from real life that needs it. > > > > > > Matthew gave an example of a real life use case and I explained why IMO > > > we don't need to add fsnotify_open() for the use case that he described. > > > > > > If you want to add fsnotify_open() to any call site, please come up with > > > a real life use case - not a made up one, one that really exists and where > > > the open event is really needed. > > > > > > grepping the code for callers of filp_open() is not enough. > > > > Yeah. So in kernel, things are both ways. There are filp_open() users that > > do take care to manually generate fsnotify_open() event (most notably > > io_uring, exec, or do_handle_open) and there are others as Xiaoming found > > which just don't bother. I'm not sure filp_open() should unconditionally > > generate fsnotify_open() event as IMO some of those notifications would be > > more confusing than useful. > > > > OTOH it is true that e.g. for core dumping we will generate other fsnotify > > events such as FSNOTIFY_CLOSE (which is generated in __fput()) so missing > > And to be fair, those kernel callers will probably also end up generating > FS_ACCESS/FS_MODIFY too. Yes. > > FSNOTIFY_OPEN is somewhat confusing. So having some consistency in this > > (either by generating FSNOTIFY_OPEN or by not generating FSNOTIFY_CLOSE) > > would be IMO desirable. > > Well, dropping events (FS_CLOSE in particular) didn't go down well the > last time we tried it: > https://lore.kernel.org/linux-fsdevel/CAOQ4uxg8E-im=B6L0PQNaTTKdtxVAO=MSJki7kxq875ME4hOLw@xxxxxxxxxxxxxx/ Right, I remember that one :) > I am just wondering who is using FS_OPEN these days and whether > they would care about this change and if not, why are we doing it? I'd be interested who is using FS_OPEN these days as well. And you're right that without users the discussion is kind of moot. > The argument that it is confusing to see FS_ACCESS/FS_MODIFY/FS_CLOSE > and not seeing FS_OPEN is only half true - it is common to see that > pattern when the file is already open when starting to watch, so application > should not break because of that pattern. Good point. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
