From patchwork Tue Jul 30 05:15:49 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Al Viro X-Patchwork-Id: 13746631 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CBBCE16C850; Tue, 30 Jul 2024 05:14:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722316489; cv=none; b=YzH+8s/wUEY6TUfpqlt/953S7+5UaEAUAhdPhEaP8eXivj+iD+5jtKkXtdseC85g9ez5x0O5oMH1yd5g4kI4ucxDOG5jxeAbhQTo/We39MV/taQ1npUQ7G3gw4B/6orWYDA/Rzo9sR37nEdXoQ2FRbc1kB7/0quBMqwTd12642Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722316489; c=relaxed/simple; bh=ZNRbrafpMZOvFmPSPkkvR42FVPPV+FlH4yiPBoNCuRQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=JJDBocgJ4xcu+fAKpGvzWheWYAYQszrnAZRojBeym9mfpBGKkj++O6Cc+eGK/HQtkckEA2xBCHJJV2nsu6imxNjfFVX8PkpScUCEBKZ+o3D1fOUJ7yr5XUY/eW4GcrrSQAr7aJ7xZgdwVJLoId7bPwIFVzXDKWSlz9wQDzV2muA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DRRt8mQj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DRRt8mQj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A510DC4AF14; Tue, 30 Jul 2024 05:14:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722316489; bh=ZNRbrafpMZOvFmPSPkkvR42FVPPV+FlH4yiPBoNCuRQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DRRt8mQjOglM7hqk7RE+FhyDRo6Q85oXP67J/+0o9/t/8DYqU2n4yS4z+tKvUx3NI 1MKUQifmSgFV/SKY6iUqttGYh1xQJe2DrzedvAK9WyohaeB+gYLH8Yukd1w6DeYgE1 0Vi57lOJ6eIngEZohLK4Bg6ya93mLVgt6RJJE8t2ECtt3+URU1fwvkOOoOKexAaPBf al6194h6yEdw7steQlLe/808A3CkpCz8z5BdHrGyZbZI4U4jlQ9aN4+XJLPGZO5jWu 9804zD9o0kxXX1GDX71+phcn+mRQpo+kQ3iVjbjApXOEgQQiJqKBpTfl1KVcYVd4JT xjJEPnFlOHmFQ== From: viro@kernel.org To: linux-fsdevel@vger.kernel.org Cc: amir73il@gmail.com, bpf@vger.kernel.org, brauner@kernel.org, cgroups@vger.kernel.org, kvm@vger.kernel.org, netdev@vger.kernel.org, torvalds@linux-foundation.org Subject: [PATCH 03/39] struct fd: representation change Date: Tue, 30 Jul 2024 01:15:49 -0400 Message-Id: <20240730051625.14349-3-viro@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240730051625.14349-1-viro@kernel.org> References: <20240730050927.GC5334@ZenIV> <20240730051625.14349-1-viro@kernel.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Al Viro The absolute majority of instances comes from fdget() and its relatives; the underlying primitives actually return a struct file reference and a couple of flags encoded into an unsigned long - the lower two bits of file address are always zero, so we can stash the flags into those. On the way out we use __to_fd() to unpack that unsigned long into struct fd. Let's use that representation for struct fd itself - make it a structure with a single unsigned long member (.word), with the value equal either to (unsigned long)p | flags, p being an address of some struct file instance, or to 0 for an empty fd. Note that we never used a struct fd instance with NULL ->file and non-zero ->flags; the emptiness had been checked as (!f.file) and we expected e.g. fdput(empty) to be a no-op. With new representation we can use (!f.word) for emptiness check; that is enough for compiler to figure out that (f.word & FDPUT_FPUT) will be false and that fdput(f) will be a no-op in such case. For now the new predicate (fd_empty(f)) has no users; all the existing checks have form (!fd_file(f)). We will convert to fd_empty() use later; here we only define it (and tell the compiler that it's unlikely to return true). This commit only deals with representation change; there will be followups. Signed-off-by: Al Viro Reviewed-by: Christian Brauner --- drivers/infiniband/core/uverbs_cmd.c | 2 +- fs/overlayfs/file.c | 28 +++++++++++++++------------- fs/xfs/xfs_handle.c | 2 +- include/linux/file.h | 22 ++++++++++++++++------ kernel/events/core.c | 2 +- net/socket.c | 2 +- 6 files changed, 35 insertions(+), 23 deletions(-) diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c index 3f85575cf971..a4cce360df21 100644 --- a/drivers/infiniband/core/uverbs_cmd.c +++ b/drivers/infiniband/core/uverbs_cmd.c @@ -572,7 +572,7 @@ static int ib_uverbs_open_xrcd(struct uverbs_attr_bundle *attrs) struct inode *inode = NULL; int new_xrcd = 0; struct ib_device *ib_dev; - struct fd f = {}; + struct fd f = EMPTY_FD; int ret; ret = uverbs_request(attrs, &cmd, sizeof(cmd)); diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index c4963d0c5549..2b7a5a3a7a2f 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -93,11 +93,11 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real, bool allow_meta) { struct dentry *dentry = file_dentry(file); + struct file *realfile = file->private_data; struct path realpath; int err; - real->flags = 0; - real->file = file->private_data; + real->word = (unsigned long)realfile; if (allow_meta) { ovl_path_real(dentry, &realpath); @@ -113,16 +113,17 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real, return -EIO; /* Has it been copied up since we'd opened it? */ - if (unlikely(file_inode(real->file) != d_inode(realpath.dentry))) { - real->flags = FDPUT_FPUT; - real->file = ovl_open_realfile(file, &realpath); - - return PTR_ERR_OR_ZERO(real->file); + if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) { + struct file *f = ovl_open_realfile(file, &realpath); + if (IS_ERR(f)) + return PTR_ERR(f); + real->word = (unsigned long)ovl_open_realfile(file, &realpath) | FDPUT_FPUT; + return 0; } /* Did the flags change since open? */ - if (unlikely((file->f_flags ^ real->file->f_flags) & ~OVL_OPEN_FLAGS)) - return ovl_change_flags(real->file, file->f_flags); + if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) + return ovl_change_flags(realfile, file->f_flags); return 0; } @@ -130,10 +131,11 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real, static int ovl_real_fdget(const struct file *file, struct fd *real) { if (d_is_dir(file_dentry(file))) { - real->flags = 0; - real->file = ovl_dir_real_file(file, false); - - return PTR_ERR_OR_ZERO(real->file); + struct file *f = ovl_dir_real_file(file, false); + if (IS_ERR(f)) + return PTR_ERR(f); + real->word = (unsigned long)f; + return 0; } return ovl_real_fdget_meta(file, real, false); diff --git a/fs/xfs/xfs_handle.c b/fs/xfs/xfs_handle.c index 7bcc4f519cb8..49e5e5f04e60 100644 --- a/fs/xfs/xfs_handle.c +++ b/fs/xfs/xfs_handle.c @@ -85,7 +85,7 @@ xfs_find_handle( int hsize; xfs_handle_t handle; struct inode *inode; - struct fd f = {NULL}; + struct fd f = EMPTY_FD; struct path path; int error; struct xfs_inode *ip; diff --git a/include/linux/file.h b/include/linux/file.h index 0f3f369f2450..bdd6e1766839 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -35,18 +35,28 @@ static inline void fput_light(struct file *file, int fput_needed) fput(file); } +/* either a reference to struct file + flags + * (cloned vs. borrowed, pos locked), with + * flags stored in lower bits of value, + * or empty (represented by 0). + */ struct fd { - struct file *file; - unsigned int flags; + unsigned long word; }; #define FDPUT_FPUT 1 #define FDPUT_POS_UNLOCK 2 -#define fd_file(f) ((f).file) +#define fd_file(f) ((struct file *)((f).word & ~3)) +static inline bool fd_empty(struct fd f) +{ + return unlikely(!f.word); +} + +#define EMPTY_FD (struct fd){0} static inline void fdput(struct fd fd) { - if (fd.flags & FDPUT_FPUT) + if (fd.word & FDPUT_FPUT) fput(fd_file(fd)); } @@ -60,7 +70,7 @@ extern void __f_unlock_pos(struct file *); static inline struct fd __to_fd(unsigned long v) { - return (struct fd){(struct file *)(v & ~3),v & 3}; + return (struct fd){v}; } static inline struct fd fdget(unsigned int fd) @@ -80,7 +90,7 @@ static inline struct fd fdget_pos(int fd) static inline void fdput_pos(struct fd f) { - if (f.flags & FDPUT_POS_UNLOCK) + if (f.word & FDPUT_POS_UNLOCK) __f_unlock_pos(fd_file(f)); fdput(f); } diff --git a/kernel/events/core.c b/kernel/events/core.c index 17b19d3e74ba..fd2ac9c7fd77 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12474,7 +12474,7 @@ SYSCALL_DEFINE5(perf_event_open, struct perf_event_attr attr; struct perf_event_context *ctx; struct file *event_file = NULL; - struct fd group = {NULL, 0}; + struct fd group = EMPTY_FD; struct task_struct *task = NULL; struct pmu *pmu; int event_fd; diff --git a/net/socket.c b/net/socket.c index f77a42a74510..c0d4f5032374 100644 --- a/net/socket.c +++ b/net/socket.c @@ -559,7 +559,7 @@ static struct socket *sockfd_lookup_light(int fd, int *err, int *fput_needed) if (fd_file(f)) { sock = sock_from_file(fd_file(f)); if (likely(sock)) { - *fput_needed = f.flags & FDPUT_FPUT; + *fput_needed = f.word & FDPUT_FPUT; return sock; } *err = -ENOTSOCK;