From: "Darrick J. Wong" <djwong@kernel.org>
To: bernd@bsbernd.com
Cc: neal@gompa.dev, fuse-devel@lists.linux.dev
Subject: Re: [PATCH 4/4] mount/fuse_service: share the service socket helpers
Date: Wed, 30 Sep 2026 08:23:42 -0700 [thread overview]
Message-ID: <20260930152342.GQ6253@frogsfrogsfrogs> (raw)
In-Reply-To: <20260930-mount-service-use-mount-fsmount-v1-4-d585598896ee@bsbernd.com>
On Wed, Sep 30, 2026 at 03:44:36PM +0200, Bernd Schubert via B4 Relay wrote:
> From: Bernd Schubert <bernd@bsbernd.com>
>
> lib/fuse_service.c and util/mount_service.c each had their own sendmsg()
> and recvmsg() for the same packets, repeating MSG_EOR|MSG_NOSIGNAL and
> MSG_TRUNC, plus their own SO_SNDBUF check. Every change to how a packet
> travels had to be made twice.
>
> fuse_service_send_packet(), fuse_service_recv_packet() and
> fuse_service_sendbuf_too_small() move to include/fuse_service_priv.h,
> which both files already include for the packet layout. The error
> messages differ per file and stay in the callers.
>
> Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
Looks good,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
--D
> ---
> include/fuse_service_priv.h | 59 +++++++++++++++++++++++++++++++++++++
> lib/fuse_service.c | 72 ++++++++++-----------------------------------
> util/mount_service.c | 59 ++++++-------------------------------
> 3 files changed, 83 insertions(+), 107 deletions(-)
>
> diff --git a/include/fuse_service_priv.h b/include/fuse_service_priv.h
> index 988f7c9251c8..951694faaaba 100644
> --- a/include/fuse_service_priv.h
> +++ b/include/fuse_service_priv.h
> @@ -9,6 +9,9 @@
> #ifndef FUSE_SERVICE_PRIV_H_
> #define FUSE_SERVICE_PRIV_H_
>
> +#include <sys/socket.h>
> +#include <limits.h>
> +
> /* All numeric fields are network order (big-endian) when going across the socket */
>
> struct fuse_service_memfd_arg {
> @@ -48,6 +51,36 @@ struct fuse_service_packet {
> uint32_t magic; /* FUSE_SERVICE_*_{CMD,REPLY} */
> };
>
> +static inline ssize_t fuse_service_send_packet(int sockfd, void *ptr,
> + size_t len)
> +{
> + struct iovec iov = {
> + .iov_base = ptr,
> + .iov_len = len,
> + };
> + struct msghdr msg = {
> + .msg_iov = &iov,
> + .msg_iovlen = 1,
> + };
> +
> + return sendmsg(sockfd, &msg, MSG_EOR | MSG_NOSIGNAL);
> +}
> +
> +static inline ssize_t fuse_service_recv_packet(int sockfd, void *ptr,
> + size_t len)
> +{
> + struct iovec iov = {
> + .iov_base = ptr,
> + .iov_len = len,
> + };
> + struct msghdr msg = {
> + .msg_iov = &iov,
> + .msg_iovlen = 1,
> + };
> +
> + return recvmsg(sockfd, &msg, MSG_TRUNC);
> +}
> +
> #define FUSE_SERVICE_PROTO (1)
> #define FUSE_SERVICE_MIN_PROTO (1)
> #define FUSE_SERVICE_MAX_PROTO (1)
> @@ -117,6 +150,32 @@ static inline size_t sizeof_fuse_service_open_command(size_t pathlen)
> return sizeof(struct fuse_service_open_command) + pathlen + 1;
> }
>
> +/*
> + * A send buffer that cannot hold the largest open command makes the sendmsg
> + * fail later on; report the size so the caller can say so in its own words.
> + * A buffer we cannot query is not an error - most likely we won't be sending
> + * huge open commands, and if we do, the sendmsg will fail there too.
> + *
> + * @sendbuf_sizep set to the offending size when the buffer is too small
> + * @return true if the send buffer is too small
> + */
> +static inline bool fuse_service_sendbuf_too_small(int sockfd,
> + int *sendbuf_sizep)
> +{
> + int sendbuf_size = -1;
> + socklen_t optlen = sizeof(sendbuf_size);
> +
> + if (getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &sendbuf_size, &optlen) ||
> + sendbuf_size < 0)
> + return false;
> +
> + if ((size_t)sendbuf_size >= sizeof_fuse_service_open_command(PATH_MAX))
> + return false;
> +
> + *sendbuf_sizep = sendbuf_size;
> + return true;
> +}
> +
> struct fuse_service_string_command {
> struct fuse_service_packet p;
> char value[];
> diff --git a/lib/fuse_service.c b/lib/fuse_service.c
> index 0a05b3fbc1f2..1f3fc1be0888 100644
> --- a/lib/fuse_service.c
> +++ b/lib/fuse_service.c
> @@ -135,36 +135,6 @@ static int __recv_fd(const struct fuse_service *sf,
> return 0;
> }
>
> -static ssize_t __send_packet(const struct fuse_service *sf, void *ptr,
> - size_t len)
> -{
> - struct iovec iov = {
> - .iov_base = ptr,
> - .iov_len = len,
> - };
> - struct msghdr msg = {
> - .msg_iov = &iov,
> - .msg_iovlen = 1,
> - };
> -
> - return sendmsg(sf->sockfd, &msg, MSG_EOR | MSG_NOSIGNAL);
> -}
> -
> -static ssize_t __recv_packet(const struct fuse_service *sf, void *ptr,
> - size_t len)
> -{
> - struct iovec iov = {
> - .iov_base = ptr,
> - .iov_len = len,
> - };
> - struct msghdr msg = {
> - .msg_iov = &iov,
> - .msg_iovlen = 1,
> - };
> -
> - return recvmsg(sf->sockfd, &msg, MSG_TRUNC);
> -}
> -
> int fuse_service_receive_file(const struct fuse_service *sf, const char *path,
> int *fdp)
> {
> @@ -266,7 +236,7 @@ static int fuse_service_request_path(const struct fuse_service *sf,
> cmd->request_flags = htonl(rqflags);
> memcpy(cmd->path, path, pathlen + 1);
>
> - size = __send_packet(sf, cmd, cmdsz);
> + size = fuse_service_send_packet(sf->sockfd, cmd, cmdsz);
> if (size < 0) {
> int error = errno;
>
> @@ -313,7 +283,7 @@ int fuse_service_send_goodbye(struct fuse_service *sf, int exitcode)
> if (sf->sockfd < 0)
> return 0;
>
> - size = __send_packet(sf, &c, sizeof(c));
> + size = fuse_service_send_packet(sf->sockfd, &c, sizeof(c));
> if (size < 0) {
> int error = errno;
>
> @@ -367,25 +337,13 @@ static int count_listen_fds(void)
>
> static int check_sendbuf_size(int sockfd)
> {
> - const size_t min_size = sizeof_fuse_service_open_command(PATH_MAX);
> - int sendbuf_size = -1;
> - socklen_t optlen = sizeof(sendbuf_size);
> - int ret;
> + int sendbuf_size;
>
> - /*
> - * If we can't query the maximum send buffer length, just keep going.
> - * Most likely we won't be sending huge open commands, and if we do,
> - * the sendmsg will fail there too.
> - */
> - ret = getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &sendbuf_size, &optlen);
> - if (ret || sendbuf_size < 0)
> - return 0;
> -
> - if (sendbuf_size >= min_size)
> + if (!fuse_service_sendbuf_too_small(sockfd, &sendbuf_size))
> return 0;
>
> fuse_log(FUSE_LOG_ERR, "max socket send buffer is %d, need at least %zu.\n",
> - sendbuf_size, min_size);
> + sendbuf_size, sizeof_fuse_service_open_command(PATH_MAX));
> return -ENOBUFS;
> }
>
> @@ -456,7 +414,7 @@ static int negotiate_hello(struct fuse_service *sf)
> uint32_t flags;
> ssize_t size;
>
> - size = __recv_packet(sf, &hello, sizeof(hello));
> + size = fuse_service_recv_packet(sf->sockfd, &hello, sizeof(hello));
> if (size < 0) {
> int error = errno;
>
> @@ -511,7 +469,7 @@ static int negotiate_hello(struct fuse_service *sf)
> if (flags & FUSE_SERVICE_FLAG_FUSEBLK)
> sf->can_fuseblk = true;
>
> - size = __send_packet(sf, &reply, sizeof(reply));
> + size = fuse_service_send_packet(sf->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> int error = errno;
>
> @@ -821,7 +779,7 @@ static int send_fsopen(const struct fuse_service *sf, const char *fstype,
> if (!strncmp(fstype, "fuseblk", 7))
> c.fsopen_flags |= htonl(FUSE_SERVICE_FSOPEN_FUSEBLK);
>
> - size = __send_packet(sf, &c, sizeof(c));
> + size = fuse_service_send_packet(sf->sockfd, &c, sizeof(c));
> if (size < 0) {
> int error = errno;
>
> @@ -830,7 +788,7 @@ static int send_fsopen(const struct fuse_service *sf, const char *fstype,
> return -error;
> }
>
> - size = __recv_packet(sf, &reply, sizeof(reply));
> + size = fuse_service_recv_packet(sf->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> int error = errno;
>
> @@ -873,7 +831,7 @@ static int send_string(const struct fuse_service *sf, uint32_t command,
> cmd->p.magic = htonl(command);
> memcpy(cmd->value, value, valuelen + 1);
>
> - size = __send_packet(sf, cmd, cmdsz);
> + size = fuse_service_send_packet(sf->sockfd, cmd, cmdsz);
> if (size < 0) {
> err = -errno;
> fuse_log(FUSE_LOG_ERR, "fuse: send service string: %s\n",
> @@ -881,7 +839,7 @@ static int send_string(const struct fuse_service *sf, uint32_t command,
> goto out;
> }
>
> - size = __recv_packet(sf, &reply, sizeof(reply));
> + size = fuse_service_recv_packet(sf->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> err = -errno;
> fuse_log(FUSE_LOG_ERR, "fuse: service string reply: %s\n",
> @@ -929,7 +887,7 @@ static int send_mountpoint(const struct fuse_service *sf, mode_t expected_fmt,
> cmd->expected_fmt = htons(expected_fmt);
> memcpy(cmd->value, value, valuelen + 1);
>
> - size = __send_packet(sf, cmd, cmdsz);
> + size = fuse_service_send_packet(sf->sockfd, cmd, cmdsz);
> if (size < 0) {
> err = -errno;
> fuse_log(FUSE_LOG_ERR, "fuse: send service mountpoint: %s\n",
> @@ -937,7 +895,7 @@ static int send_mountpoint(const struct fuse_service *sf, mode_t expected_fmt,
> goto out;
> }
>
> - size = __recv_packet(sf, &reply, sizeof(reply));
> + size = fuse_service_recv_packet(sf->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> err = -errno;
> fuse_log(FUSE_LOG_ERR, "fuse: service mountpoint reply: %s\n",
> @@ -975,7 +933,7 @@ static int send_mount(const struct fuse_service *sf, unsigned int ms_flags,
> };
> ssize_t size;
>
> - size = __send_packet(sf, &c, sizeof(c));
> + size = fuse_service_send_packet(sf->sockfd, &c, sizeof(c));
> if (size < 0) {
> int error = errno;
>
> @@ -984,7 +942,7 @@ static int send_mount(const struct fuse_service *sf, unsigned int ms_flags,
> return -error;
> }
>
> - size = __recv_packet(sf, &reply, sizeof(reply));
> + size = fuse_service_recv_packet(sf->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> int error = errno;
>
> diff --git a/util/mount_service.c b/util/mount_service.c
> index dcdc26df1db4..47cc2d43d2a0 100644
> --- a/util/mount_service.c
> +++ b/util/mount_service.c
> @@ -139,21 +139,6 @@ static ssize_t __send_fd(const struct mount_service *mo,
> return sendmsg(mo->sockfd, &msg, MSG_EOR | MSG_NOSIGNAL);
> }
>
> -static ssize_t __send_packet(const struct mount_service *mo, void *ptr,
> - size_t len)
> -{
> - struct iovec iov = {
> - .iov_base = ptr,
> - .iov_len = len,
> - };
> - struct msghdr msg = {
> - .msg_iov = &iov,
> - .msg_iovlen = 1,
> - };
> -
> - return sendmsg(mo->sockfd, &msg, MSG_EOR | MSG_NOSIGNAL);
> -}
> -
> static ssize_t __recv_packet_size(const struct mount_service *mo)
> {
> struct iovec iov = { };
> @@ -164,21 +149,6 @@ static ssize_t __recv_packet_size(const struct mount_service *mo)
> return recvmsg(mo->sockfd, &msg, MSG_PEEK | MSG_TRUNC);
> }
>
> -static ssize_t __recv_packet(const struct mount_service *mo, void *ptr,
> - size_t len)
> -{
> - struct iovec iov = {
> - .iov_base = ptr,
> - .iov_len = len,
> - };
> - struct msghdr msg = {
> - .msg_iov = &iov,
> - .msg_iovlen = 1,
> - };
> -
> - return recvmsg(mo->sockfd, &msg, MSG_TRUNC);
> -}
> -
> /*
> * Filter out the subtype of the filesystem (e.g. fuse.Y[.Z] -> Y[.Z]). The
> * fuse server determines if it's appropriate to set the "blockdev" mount
> @@ -271,25 +241,14 @@ static int try_drop_passrights(const struct mount_service *mo, int sockfd)
>
> static int check_sendbuf_size(const struct mount_service *mo, int sockfd)
> {
> - const size_t min_size = sizeof_fuse_service_open_command(PATH_MAX);
> - int sendbuf_size = -1;
> - socklen_t optlen = sizeof(sendbuf_size);
> - int ret;
> + int sendbuf_size;
>
> - /*
> - * If we can't query the maximum send buffer length, just keep going.
> - * Most likely we won't be sending huge open commands, and if we do,
> - * the sendmsg will fail there too.
> - */
> - ret = getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &sendbuf_size, &optlen);
> - if (ret || sendbuf_size < 0)
> - return 0;
> -
> - if (sendbuf_size >= min_size)
> + if (!fuse_service_sendbuf_too_small(sockfd, &sendbuf_size))
> return 0;
>
> fprintf(stderr, "%s: max socket send buffer is %d, need at least %zu.\n",
> - mo->msgtag, sendbuf_size, min_size);
> + mo->msgtag, sendbuf_size,
> + sizeof_fuse_service_open_command(PATH_MAX));
> return MOUNT_SERVICE_FALLBACK_NEEDED;
> }
>
> @@ -369,14 +328,14 @@ static int mount_service_send_hello(const struct mount_service *mo)
> else if (user_allow_other)
> hello.flags |= htonl(FUSE_SERVICE_FLAG_ALLOW_OTHER);
>
> - size = __send_packet(mo, &hello, sizeof(hello));
> + size = fuse_service_send_packet(mo->sockfd, &hello, sizeof(hello));
> if (size < 0) {
> fprintf(stderr, "%s: send hello: %s\n",
> mo->msgtag, strerror(errno));
> return -1;
> }
>
> - size = __recv_packet(mo, &reply, sizeof(reply));
> + size = fuse_service_recv_packet(mo->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> fprintf(stderr, "%s: hello reply: %s\n",
> mo->msgtag, strerror(errno));
> @@ -581,7 +540,7 @@ static int mount_service_send_file_error(const struct mount_service *mo,
> req->error = htonl(error);
> memcpy(req->path, path, path_len + 1);
>
> - written = __send_packet(mo, req, req_sz);
> + written = fuse_service_send_packet(mo->sockfd, req, req_sz);
> if (written < 0) {
> fprintf(stderr, "%s: send file error: %s\n",
> mo->msgtag, strerror(errno));
> @@ -671,7 +630,7 @@ static int mount_service_receive_command(const struct mount_service *mo,
> return -1;
> }
>
> - size = __recv_packet(mo, command, alleged_size);
> + size = fuse_service_recv_packet(mo->sockfd, command, alleged_size);
> if (size < 0) {
> fprintf(stderr, "%s: receive service command: %s\n",
> mo->msgtag, strerror(errno));
> @@ -698,7 +657,7 @@ static int mount_service_send_reply(const struct mount_service *mo, int error)
> };
> ssize_t size;
>
> - size = __send_packet(mo, &reply, sizeof(reply));
> + size = fuse_service_send_packet(mo->sockfd, &reply, sizeof(reply));
> if (size < 0) {
> fprintf(stderr, "%s: send service reply: %s\n",
> mo->msgtag, strerror(errno));
>
> --
> 2.53.0
>
>
>
prev parent reply other threads:[~2026-09-30 15:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 13:44 [PATCH 0/4] libfuse: Avoid mount API code dup between mount-service and libfuse Bernd Schubert via B4 Relay
2026-09-30 13:44 ` [PATCH 1/4] mount_fsmount: split superblock creation and move_mount into a helper Bernd Schubert via B4 Relay
2026-09-30 15:13 ` Darrick J. Wong
2026-09-30 13:44 ` [PATCH 2/4] mount_service: mount via the shared fsmount helper Bernd Schubert via B4 Relay
2026-09-30 15:16 ` Darrick J. Wong
2026-09-30 13:44 ` [PATCH 3/4] mount_util: share the mtab flag-option builder Bernd Schubert via B4 Relay
2026-09-30 15:20 ` Darrick J. Wong
2026-09-30 13:44 ` [PATCH 4/4] mount/fuse_service: share the service socket helpers Bernd Schubert via B4 Relay
2026-09-30 15:23 ` Darrick J. Wong [this message]
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