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Date: Thu, 12 Aug 2021 16:20:47 +0200 From: Jan Kara <jack@...e.cz> To: Gabriel Krisman Bertazi <krisman@...labora.com> Cc: Jan Kara <jack@...e.cz>, jack@...e.com, amir73il@...il.com, djwong@...nel.org, tytso@....edu, david@...morbit.com, dhowells@...hat.com, khazhy@...gle.com, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-api@...r.kernel.org, kernel@...labora.com Subject: Re: [PATCH v5 14/23] fanotify: Encode invalid file handler when no inode is provided On Wed 11-08-21 17:12:05, Gabriel Krisman Bertazi wrote: > Jan Kara <jack@...e.cz> writes: > >> @@ -376,14 +371,24 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, > >> fh->flags |= FANOTIFY_FH_FLAG_EXT_BUF; > >> } > >> > >> - dwords = fh_len >> 2; > >> - type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL); > >> - err = -EINVAL; > >> - if (!type || type == FILEID_INVALID || fh_len != dwords << 2) > >> - goto out_err; > >> - > >> - fh->type = type; > >> - fh->len = fh_len; > >> + if (inode) { > >> + dwords = fh_len >> 2; > >> + type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL); > >> + err = -EINVAL; > >> + if (!type || type == FILEID_INVALID || fh_len != dwords << 2) > >> + goto out_err; > >> + fh->type = type; > >> + fh->len = fh_len; > >> + } else { > >> + /* > >> + * Invalid FHs are used on FAN_FS_ERROR for errors not > >> + * linked to any inode. Caller needs to guarantee the fh > >> + * has at least FANOTIFY_NULL_FH_LEN bytes of space. > >> + */ > >> + fh->type = FILEID_INVALID; > >> + fh->len = FANOTIFY_NULL_FH_LEN; > >> + memset(buf, 0, FANOTIFY_NULL_FH_LEN); > >> + } > > > > Maybe it will become clearer later during the series but why do you set > > fh->len to FANOTIFY_NULL_FH_LEN and not 0? > > Jan, > > That is how we encode a NULL file handle (i.e. superblock error). Amir > suggested it would be an invalid FILEID_INVALID, with a zeroed handle of > size 8. I will improve the comment on the next iteration. Thanks for info. Then I have a question for Amir I guess :) Amir, what's the advantage of zeroed handle of size 8 instead of just 0 length file handle? Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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