linux-ext4 - Re: [PATCH v7 23/28] fanotify: Report fid info for file related file system errors

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Date:   Fri, 15 Oct 2021 10:56:38 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com
Subject: Re: [PATCH v7 23/28] fanotify: Report fid info for file related file
 system errors

On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Plumb the pieces to add a FID report to error records.  Since all error
> event memory must be pre-allocated, we pre-allocate the maximum file
> handle size possible, such that it should always fit.
>
> For errors that don't expose a file handle report it with an invalid
> FID.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>
> ---
> Changes since v6:
>   - pass fsid from handle_events
> Changes since v5:
>   - Use preallocated MAX_HANDLE_SZ FH buffer
>   - Report superblock errors with a zerolength INVALID FID (jan, amir)
> ---
>  fs/notify/fanotify/fanotify.c | 15 +++++++++++++++
>  fs/notify/fanotify/fanotify.h |  8 ++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 7032083df62a..8a60c96f5fb2 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -611,7 +611,9 @@ static struct fanotify_event *fanotify_alloc_error_event(
>  {
>         struct fs_error_report *report =
>                         fsnotify_data_error_report(data, data_type);
> +       struct inode *inode = report->inode;
>         struct fanotify_error_event *fee;
> +       int fh_len;
>
>         if (WARN_ON(!report))
>                 return NULL;
> @@ -622,6 +624,19 @@ static struct fanotify_event *fanotify_alloc_error_event(
>
>         fee->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
>         fee->err_count = 1;
> +       fee->fsid = *fsid;
> +
> +       fh_len = fanotify_encode_fh_len(inode);
> +       if (WARN_ON(fh_len > MAX_HANDLE_SZ)) {

WARN_ON_ONCE please and I rather that this sanity check is moved inside
fanotify_encode_fh_len() where it will return 0 for encoding failure.

> +               /*
> +                * Fallback to reporting the error against the super
> +                * block.  It should never happen.
> +                */
> +               inode = NULL;
> +               fh_len = fanotify_encode_fh_len(NULL);
> +       }
> +
> +       fanotify_encode_fh(&fee->object_fh, inode, fh_len, NULL, 0);
>
>         *hash ^= fanotify_hash_fsid(fsid);
>
> diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> index 2b032b79d5b0..b58400926f92 100644
> --- a/fs/notify/fanotify/fanotify.h
> +++ b/fs/notify/fanotify/fanotify.h
> @@ -202,6 +202,10 @@ struct fanotify_error_event {
>         u32 err_count; /* Suppressed errors count */
>
>         __kernel_fsid_t fsid; /* FSID this error refers to. */
> +       /* object_fh must be followed by the inline handle buffer. */
> +       struct fanotify_fh object_fh;
> +       /* Reserve space in object_fh.buf[] - access with fanotify_fh_buf() */
> +       unsigned char _inline_fh_buf[MAX_HANDLE_SZ];
>  };

This struct duplicates most of struct fanotify_fid_event.
How about:

#define FANOTIFY_ERROR_FH_LEN \
             (MAX_HANDLE_SZ - FANOTIFY_INLINE_FH_LEN)

struct fanotify_error_event {
         u32 err_count; /* Suppressed errors count */
         struct fanotify_event ffe;
         /* Reserve space in ffe.object_fh.buf[] - access with
fanotify_fh_buf() */
         unsigned char _fh_buf[FANOTIFY_ERROR_FH_LEN];
}

Or leaving out the struct padding and passing
FANOTIFY_ERROR_EVENT_SIZE as mempool object size?

#define FANOTIFY_ERROR_EVENT_SIZE \
            (sizeof(struct fanotify_error_event) + FANOTIFY_ERROR_FH_LEN)

You do not have to make this change - it is a proposal that can have
supporters and objectors, so let's wait to see what you and other reviewers
have to say.

Thanks,
Amir.