On Sun, Mar 16, 2025 at 01:30:20AM +0800, saz97 wrote:
> Signed-off-by: Changzhi Xie <s...@qq.com>
>
> This commit refactors the FUSE export to process read and write operations
> using coroutines, improving concurrency and avoiding blocking the main loop.
>
> The main changes include:
> 1. Introduce FuseIORequest structure to encapsulate I/O parameters and state
> 2. Move read/write processing into coroutine fuse_read_coroutine and
> fuse_write_coroutine
> 3. Use blk_co_pread/pwrite for async block layer access
> ---
> block/export/fuse.c | 189 +++++++++++++++++++++++++++++++-------------
> 1 file changed, 132 insertions(+), 57 deletions(-)
>
> diff --git a/block/export/fuse.c b/block/export/fuse.c
> index 465cc9891d..3314f64706 100644
> --- a/block/export/fuse.c
> +++ b/block/export/fuse.c
> @@ -39,6 +39,7 @@
>
> #ifdef __linux__
> #include <linux/fs.h>
> +#include <linux/fuse.h>
> #endif
>
> /* Prevent overly long bounce buffer allocations */
> @@ -49,7 +50,6 @@ typedef struct FuseExport {
> BlockExport common;
>
> struct fuse_session *fuse_session;
> - struct fuse_buf fuse_buf;
> unsigned int in_flight; /* atomic */
> bool mounted, fd_handler_set_up;
>
> @@ -64,6 +64,14 @@ typedef struct FuseExport {
> gid_t st_gid;
> } FuseExport;
>
> +typedef struct FuseIORequest {
> + fuse_req_t req;
> + size_t size;
> + off_t offset;
> + FuseExport *exp;
> + char *write_buf;
> +} FuseIORequest;
> +
> static GHashTable *exports;
> static const struct fuse_lowlevel_ops fuse_ops;
>
> @@ -288,6 +296,7 @@ fail:
> static void read_from_fuse_export(void *opaque)
> {
> FuseExport *exp = opaque;
> + struct fuse_buf buf = {};
> int ret;
>
> blk_exp_ref(&exp->common);
> @@ -295,20 +304,30 @@ static void read_from_fuse_export(void *opaque)
> qatomic_inc(&exp->in_flight);
>
> do {
> - ret = fuse_session_receive_buf(exp->fuse_session, &exp->fuse_buf);
> + ret = fuse_session_receive_buf(exp->fuse_session, &buf);
> } while (ret == -EINTR);
> if (ret < 0) {
> goto out;
> }
>
> - fuse_session_process_buf(exp->fuse_session, &exp->fuse_buf);
> + fuse_session_process_buf(exp->fuse_session, &buf);
>
> out:
> + struct fuse_in_header *in = (struct fuse_in_header *)buf.mem;
> +
> + if (in->opcode == FUSE_WRITE || in->opcode == FUSE_READ) {
> + g_free(buf.mem);
> + return;
Returning here is not safe because &buf was passed to
fuse_session_process_buf() and is located on read_from_fuse_export()'s
stack. The coroutine must not access buf after this function returns.
I suggest moving most of this function into a coroutine so that struct
fuse_buf can be on the coroutine's stack. That way it outlives
fuse_session_process_buf().
Doing this also avoids duplicating the code below and eliminates the
need for FuseIORequest.
> + }
> +
> if (qatomic_fetch_dec(&exp->in_flight) == 1) {
> aio_wait_kick(); /* wake AIO_WAIT_WHILE() */
> }
>
> blk_exp_unref(&exp->common);
> +
> + g_free(buf.mem);
Please make this free(buf.mem) since libfuse uses malloc(3).
> +
> }
>
> static void fuse_export_shutdown(BlockExport *blk_exp)
> @@ -347,7 +366,6 @@ static void fuse_export_delete(BlockExport *blk_exp)
> fuse_session_destroy(exp->fuse_session);
> }
>
> - free(exp->fuse_buf.mem);
> g_free(exp->mountpoint);
> }
>
> @@ -570,102 +588,159 @@ static void fuse_open(fuse_req_t req, fuse_ino_t
> inode,
> fuse_reply_open(req, fi);
> }
>
> -/**
> - * Handle client reads from the exported image.
> - */
> -static void fuse_read(fuse_req_t req, fuse_ino_t inode,
> - size_t size, off_t offset, struct fuse_file_info *fi)
> +static void coroutine_fn fuse_read_coroutine(void *opaque)
> {
> - FuseExport *exp = fuse_req_userdata(req);
> + FuseIORequest *io_req = opaque;
> + FuseExport *exp = io_req->exp;
> int64_t length;
> - void *buf;
> + void *buffer;
> int ret;
>
> - /* Limited by max_read, should not happen */
> - if (size > FUSE_MAX_BOUNCE_BYTES) {
> - fuse_reply_err(req, EINVAL);
> - return;
> + if (io_req->size > FUSE_MAX_BOUNCE_BYTES) {
> + fuse_reply_err(io_req->req, EINVAL);
> + goto cleanup;
> }
>
> - /**
> - * Clients will expect short reads at EOF, so we have to limit
> - * offset+size to the image length.
> - */
> length = blk_getlength(exp->common.blk);
> if (length < 0) {
> - fuse_reply_err(req, -length);
> - return;
> + fuse_reply_err(io_req->req, -length);
> + goto cleanup;
> }
>
> - if (offset + size > length) {
> - size = length - offset;
> + if (io_req->offset + io_req->size > length) {
> + io_req->size = length - io_req->offset;
> }
>
> - buf = qemu_try_blockalign(blk_bs(exp->common.blk), size);
> - if (!buf) {
> - fuse_reply_err(req, ENOMEM);
> - return;
> + if (io_req->size == 0) {
> + fuse_reply_buf(io_req->req, NULL, 0);
> + goto cleanup;
> }
>
> - ret = blk_pread(exp->common.blk, offset, size, buf, 0);
> + buffer = qemu_try_blockalign(blk_bs(exp->common.blk), io_req->size);
> + if (!buffer) {
> + fuse_reply_err(io_req->req, ENOMEM);
> + goto cleanup;
> + }
> +
> + ret = blk_co_pread(exp->common.blk, io_req->offset,
> + io_req->size, buffer, 0);
> if (ret >= 0) {
> - fuse_reply_buf(req, buf, size);
> + fuse_reply_buf(io_req->req, buffer, io_req->size);
> } else {
> - fuse_reply_err(req, -ret);
> + fuse_reply_err(io_req->req, -ret);
> + }
> +
> + qemu_vfree(buffer);
> +
> +cleanup:
> + if (qatomic_fetch_dec(&exp->in_flight) == 1) {
> + aio_wait_kick(); /* wake AIO_WAIT_WHILE() */
> }
>
> - qemu_vfree(buf);
> + blk_exp_unref(&exp->common);
> +
> + g_free(io_req);
> }
>
> -/**
> - * Handle client writes to the exported image.
> - */
> -static void fuse_write(fuse_req_t req, fuse_ino_t inode, const char *buf,
> - size_t size, off_t offset, struct fuse_file_info *fi)
> +static void coroutine_fn fuse_write_coroutine(void *opaque)
> {
> - FuseExport *exp = fuse_req_userdata(req);
> + FuseIORequest *io_req = opaque;
> + FuseExport *exp = io_req->exp;
> int64_t length;
> int ret;
>
> - /* Limited by max_write, should not happen */
> - if (size > BDRV_REQUEST_MAX_BYTES) {
> - fuse_reply_err(req, EINVAL);
> - return;
> + if (io_req->size > BDRV_REQUEST_MAX_BYTES) {
> + fuse_reply_err(io_req->req, EINVAL);
> + goto cleanup;
> }
>
> if (!exp->writable) {
> - fuse_reply_err(req, EACCES);
> - return;
> + fuse_reply_err(io_req->req, EACCES);
> + goto cleanup;
> }
>
> - /**
> - * Clients will expect short writes at EOF, so we have to limit
> - * offset+size to the image length.
> - */
> length = blk_getlength(exp->common.blk);
> if (length < 0) {
> - fuse_reply_err(req, -length);
> - return;
> + fuse_reply_err(io_req->req, -length);
> + goto cleanup;
> }
>
> - if (offset + size > length) {
> + if (io_req->offset + io_req->size > length) {
> if (exp->growable) {
> - ret = fuse_do_truncate(exp, offset + size, true,
> PREALLOC_MODE_OFF);
> + ret = fuse_do_truncate(exp, io_req->offset + io_req->size,
> + true, PREALLOC_MODE_OFF);
> if (ret < 0) {
> - fuse_reply_err(req, -ret);
> - return;
> + fuse_reply_err(io_req->req, -ret);
> + goto cleanup;
> }
> } else {
> - size = length - offset;
> + io_req->size = MAX(0, length - io_req->offset);
> + if (io_req->size == 0) {
> + fuse_reply_write(io_req->req, 0);
> + goto cleanup;
> + }
> }
> }
>
> - ret = blk_pwrite(exp->common.blk, offset, size, buf, 0);
> + ret = blk_co_pwrite(exp->common.blk, io_req->offset, io_req->size,
> + io_req->write_buf, 0);
> if (ret >= 0) {
> - fuse_reply_write(req, size);
> + fuse_reply_write(io_req->req, io_req->size);
> } else {
> - fuse_reply_err(req, -ret);
> + fuse_reply_err(io_req->req, -ret);
> + }
> +
> +cleanup:
> + if (qatomic_fetch_dec(&exp->in_flight) == 1) {
> + aio_wait_kick(); /* wake AIO_WAIT_WHILE() */
> }
> +
> + blk_exp_unref(&exp->common);
> +
> + g_free(io_req->write_buf);
> + g_free(io_req);
> +}
> +
> +/**
> + * Handle client reads from the exported image.
> + */
> +static void fuse_read(fuse_req_t req, fuse_ino_t inode,
> + size_t size, off_t offset, struct fuse_file_info *fi)
> +{
> + FuseExport *exp = fuse_req_userdata(req);
> + FuseIORequest *io_req = g_new(FuseIORequest, 1);
> +
> + *io_req = (FuseIORequest) {
> + .req = req,
> + .size = size,
> + .offset = offset,
> + .exp = exp,
> + };
> +
> + Coroutine *co = qemu_coroutine_create(fuse_read_coroutine, io_req);
> + qemu_coroutine_enter(co);
> +}
> +
> +
> +/**
> + * Handle client writes to the exported image.
> + */
> +static void fuse_write(fuse_req_t req, fuse_ino_t inode, const char *buf,
> + size_t size, off_t offset, struct fuse_file_info *fi)
> +{
> + FuseExport *exp = fuse_req_userdata(req);
> + FuseIORequest *io_req = g_new(FuseIORequest, 1);
> +
> + *io_req = (FuseIORequest) {
> + .req = req,
> + .size = size,
> + .offset = offset,
> + .exp = exp,
> + .write_buf = g_memdup2_qemu(buf, size),
> + };
> +
> + Coroutine *co = qemu_coroutine_create(fuse_write_coroutine, io_req);
> + qemu_coroutine_enter(co);
> }
>
> /**
> --
> 2.34.1
>
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