From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lamorak.hansenpartnership.com (lamorak.hansenpartnership.com [198.37.111.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 79A0F14AD29; Wed, 19 Mar 2025 18:45:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.37.111.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742409957; cv=none; b=AFBI1a0TAYXk3hTlWJHfBHuUjyMGV2XKCHRsoG3CO4wfpcZ855HFl6IZ9eJMFDjOpazUm0GQz/S3JGlCpeaO+hvcKj4oRK6KhR9uvZ+4CxRMrHX6+PijD0zQPChltioSXBq9vCpCzBSo/GVhVVT0ApJfpjYMKWIisalW1qBNraY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742409957; c=relaxed/simple; bh=jmYzgtTRkcsqHiNNpg4VW93gtX90O8mign3nhlF50Ew=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; 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 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-03-19 at 12:46 -0400, James Bottomley wrote: > I assume you won't like the way I have to allocate and toss a cursor > for each iteration, nor the fact that there's still the > cond_resched() in there?=C2=A0 I think I can fix that but I'd have to > slice apart simple_positive(), which is a bigger undertaking. So this is what I think that would look like: it still exports the same simple_next_child() function but doesn't need to allocate cursors or do any of the cond_resched() stuff. The down side is that the slice is a lot less easily verified than the other two patches, so this one's going to need a lot of code inspection to make sure I got it right. Regards, James --- fs/libfs.c | 85 +++++++++++++++++++++++++++++++++++++++------- include/linux/fs.h | 2 ++ 2 files changed, 74 insertions(+), 13 deletions(-) diff --git a/fs/libfs.c b/fs/libfs.c index 8444f5cc4064..3a32910f44dc 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -101,6 +101,34 @@ int dcache_dir_close(struct inode *inode, struct file *file) } EXPORT_SYMBOL(dcache_dir_close); =20 +/* + * helper for positive scanning. Requires a nested while loop which shoul= d + * be broken if this returns false + */ +static bool internal_scan_positive(struct hlist_node **p, struct dentry *d= , + struct dentry **found, loff_t *count) +{ + while (*p) { + p =3D &d->d_sib.next; + + // we must at least skip cursors, to avoid livelocks + if (d->d_flags & DCACHE_DENTRY_CURSOR) + continue; + + if (simple_positive(d) && !--*count) { + spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED); + if (simple_positive(d)) + *found =3D dget_dlock(d); + spin_unlock(&d->d_lock); + if (likely(*found)) + return true; + *count =3D 1; + } + return false; + } + return true; +} + /* parent is locked at least shared */ /* * Returns an element of siblings' list. @@ -118,19 +146,9 @@ static struct dentry *scan_positives(struct dentry *cu= rsor, spin_lock(&dentry->d_lock); while (*p) { struct dentry *d =3D hlist_entry(*p, struct dentry, d_sib); - p =3D &d->d_sib.next; - // we must at least skip cursors, to avoid livelocks - if (d->d_flags & DCACHE_DENTRY_CURSOR) - continue; - if (simple_positive(d) && !--count) { - spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED); - if (simple_positive(d)) - found =3D dget_dlock(d); - spin_unlock(&d->d_lock); - if (likely(found)) - break; - count =3D 1; - } + + if (internal_scan_positive(p, d, &found, &count)) + break; if (need_resched()) { if (!hlist_unhashed(&cursor->d_sib)) __hlist_del(&cursor->d_sib); @@ -146,6 +164,47 @@ static struct dentry *scan_positives(struct dentry *cu= rsor, return found; } =20 +/** + * simple_next_child - get next child of the parent directory + * + * @parent: the directory to scan + * @child: last child (or NULL to start at the beginning) + * + * returns the next positive child in sequence with the reference + * elevated but if a child is passed in will drop that + * reference. Returns NULL on either error or when directory has been + * fully scanned. + * + * The intended use is as an iterator because all the references will + * be dropped by the end of the while loop: + * + * child =3D NULL + * while(child =3D simple_next_child(parent, child)) { + * // do something + * } + */ +struct dentry *simple_next_child(struct dentry *parent, struct dentry *chi= ld) +{ + struct hlist_node **p; + loff_t count =3D 1; + struct dentry *found =3D NULL; + + if (child) + p =3D &child->d_sib.next; + else + p =3D &parent->d_children.first; + + while (*p) { + struct dentry *d =3D hlist_entry(*p, struct dentry, d_sib); + + if (internal_scan_positive(p, d, &found, &count)) + break; + } + dput(child); + return found; +} +EXPORT_SYMBOL(simple_next_child); + loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence) { struct dentry *dentry =3D file->f_path.dentry; diff --git a/include/linux/fs.h b/include/linux/fs.h index 2788df98080f..dd84d1c3b8af 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -3531,6 +3531,8 @@ extern int simple_rename(struct mnt_idmap *, struct i= node *, unsigned int); extern void simple_recursive_removal(struct dentry *, void (*callback)(struct dentry *)); +extern struct dentry *simple_next_child(struct dentry *parent, + struct dentry *child); extern int noop_fsync(struct file *, loff_t, loff_t, int); extern ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter); extern int simple_empty(struct dentry *); --=20 2.43.0