Jan Kara <jack@xxxxxxx> writes: > On Mon 16-08-21 14:41:03, Darrick J. Wong wrote: >> On Thu, Aug 12, 2021 at 05:40:07PM -0400, Gabriel Krisman Bertazi wrote: >> > The Error info type is a record sent to users on FAN_FS_ERROR events >> > documenting the type of error. It also carries an error count, >> > documenting how many errors were observed since the last reporting. >> > >> > Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> >> > >> > --- >> > Changes since v5: >> > - Move error code here >> > --- >> > fs/notify/fanotify/fanotify.c | 1 + >> > fs/notify/fanotify/fanotify.h | 1 + >> > fs/notify/fanotify/fanotify_user.c | 36 ++++++++++++++++++++++++++++++ >> > include/uapi/linux/fanotify.h | 7 ++++++ >> > 4 files changed, 45 insertions(+) >> >> <snip> >> >> > diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h >> > index 16402037fc7a..80040a92e9d9 100644 >> > --- a/include/uapi/linux/fanotify.h >> > +++ b/include/uapi/linux/fanotify.h >> > @@ -124,6 +124,7 @@ struct fanotify_event_metadata { >> > #define FAN_EVENT_INFO_TYPE_FID 1 >> > #define FAN_EVENT_INFO_TYPE_DFID_NAME 2 >> > #define FAN_EVENT_INFO_TYPE_DFID 3 >> > +#define FAN_EVENT_INFO_TYPE_ERROR 4 >> > >> > /* Variable length info record following event metadata */ >> > struct fanotify_event_info_header { >> > @@ -149,6 +150,12 @@ struct fanotify_event_info_fid { >> > unsigned char handle[0]; >> > }; >> > >> > +struct fanotify_event_info_error { >> > + struct fanotify_event_info_header hdr; >> > + __s32 error; >> > + __u32 error_count; >> > +}; >> >> My apologies for not having time to review this patchset since it was >> redesigned to use fanotify. Someday it would be helpful to be able to >> export more detailed error reports from XFS, but as I'm not ready to >> move forward and write that today, I'll try to avoid derailling this at >> the last minute. > > I think we are not quite there and tweaking the passed structure is easy > enough so no worries. Eventually, passing some filesystem-specific blob > together with the event was the plan AFAIR. You're right now is a good > moment to think how exactly we want that passed. > >> Eventually, XFS might want to be able to report errors in file data, >> file metadata, allocation group metadata, and whole-filesystem metadata. >> Userspace can already gather reports from XFS about corruptions reported >> by the online fsck code (see xfs_health.c). > > Yes, although note that the current plan is that we currently have only one > error event queue, others are just added to error_count until the event is > fetched by userspace (on the grounds that the first error is usually the > most meaningful, the others are usually just cascading problems). But I'm > not sure if this scheme would be suitable for online fsck usecase since we > may discard even valid independent errors this way. > >> I /think/ we could subclass the file error structure that you've >> provided like so: >> >> struct fanotify_event_info_xfs_filesystem_error { >> struct fanotify_event_info_error base; >> >> __u32 magic; /* 0x58465342 to identify xfs */ >> __u32 type; /* quotas, realtime bitmap, etc. */ >> }; >> >> struct fanotify_event_info_xfs_perag_error { >> struct fanotify_event_info_error base; >> >> __u32 magic; /* 0x58465342 to identify xfs */ >> __u32 type; /* agf, agi, agfl, bno btree, ino btree, etc. */ >> __u32 agno; /* allocation group number */ >> }; >> >> struct fanotify_event_info_xfs_file_error { >> struct fanotify_event_info_error base; >> >> __u32 magic; /* 0x58465342 to identify xfs */ >> __u32 type; /* extent map, dir, attr, etc. */ >> __u64 offset; /* file data offset, if applicable */ >> __u64 length; /* file data length, if applicable */ >> }; >> >> (A real XFS implementation might have one structure with the type code >> providing for a tagged union or something; I split it into three >> separate structs here to avoid confusing things.) > > The structure of fanotify event as passed to userspace generally is: > > struct fanotify_event_metadata { > __u32 event_len; > __u8 vers; > __u8 reserved; > __u16 metadata_len; > __aligned_u64 mask; > __s32 fd; > __s32 pid; > }; > > If event_len is > sizeof(struct fanotify_event_metadata), userspace is > expected to look for struct fanotify_event_info_header after struct > fanotify_event_metadata. struct fanotify_event_info_header looks like: > > struct fanotify_event_info_header { > __u8 info_type; > __u8 pad; > __u16 len; > }; > > Again if the end of this info (defined by 'len') is smaller than > 'event_len', there is next header with next payload of data. So for example > error event will have: > > struct fanotify_event_metadata > struct fanotify_event_info_error > struct fanotify_event_info_fid > > Now either we could add fs specific blob into fanotify_event_info_error > (but then it would be good to add 'magic' to fanotify_event_info_error now > and define that if 'len' is larger, fs-specific blob follows after fixed > data) or we can add another info type FAN_EVENT_INFO_TYPE_ERROR_FS_DATA > (i.e., attach another structure into the event) which would contain the > 'magic' and then blob of data. I don't have strong preference. In the v1 of this patchset [1] I implemented the later option, a new info type that the filesystem could provide as a blob. It was dropped by Amir's request to leave it out of the discussion at that moment. Should I ressucitate it for the next iteration? I believe it would attend to XFS needs. [1] https://lwn.net/ml/linux-fsdevel/20210426184201.4177978-12-krisman@xxxxxxxxxxxxx/ -- Gabriel Krisman Bertazi