[PATCH v4] erofs-utils: add support for fuse 2/3 lowlevel API

Yue Hu zbestahu at gmail.com
Thu Aug 10 16:21:49 AEST 2023


Hi Yiyan,

Sorry for the late reply, please check some comments below.

On Thu, 27 Jul 2023 16:00:55 +0800
Li Yiyan <lyy0627 at sjtu.edu.cn> wrote:

> Add support for fuse2/3 lowlevel API in erofsfuse, pass the make check
> test in experimental-test branch. Conduct performance evaluation,
> providing higher performance compared to highlevel API. Compatible with
> fuse 2(>=2.6) and 3(>=3.0)
> 
> Signed-off-by: Li Yiyan <lyy0627 at sjtu.edu.cn>
> ---
> Changes since v3:
> - remove ll identifier
> - optimize naming
> - remove redundant log
> - add fixme label for confusing xattr_buf
> 
> Changes since v2:
> - merge lowlevel.c into main.c
> - fix typo in autoconf
> - optimize naming
> - remove redundant code
> - avoid global sbi dependencies
> 
> Changes since v1:
> - remove highlevel fallback path
> - remove redundant code
> - add static for erofsfuse_ll_func
> ---
>  configure.ac     |  23 +-
>  fuse/Makefile.am |   4 +-
>  fuse/main.c      | 605 +++++++++++++++++++++++++++++++++++++----------
>  3 files changed, 505 insertions(+), 127 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index a8cecd0..6d08d96 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -336,15 +336,26 @@ AS_IF([test "x$with_selinux" != "xno"], [
>  
>  # Configure fuse
>  AS_IF([test "x$enable_fuse" != "xno"], [
> -  PKG_CHECK_MODULES([libfuse], [fuse >= 2.6])
>    # Paranoia: don't trust the result reported by pkgconfig before trying out
>    saved_LIBS="$LIBS"
>    saved_CPPFLAGS=${CPPFLAGS}
> -  CPPFLAGS="${libfuse_CFLAGS} ${CPPFLAGS}"
> -  LIBS="${libfuse_LIBS} $LIBS"
> -  AC_CHECK_LIB(fuse, fuse_main, [
> -    have_fuse="yes" ], [
> -    AC_MSG_ERROR([libfuse (>= 2.6) doesn't work properly])])
> +  PKG_CHECK_MODULES([libfuse3], [fuse3 >= 3.0], [
> +    AC_DEFINE([FUSE_USE_VERSION], [30], [used FUSE API version])
> +    CPPFLAGS="${libfuse3_CFLAGS} ${CPPFLAGS}"
> +    LIBS="${libfuse3_LIBS} $LIBS"
> +    AC_CHECK_LIB(fuse3, fuse_session_new, [], [
> +    AC_MSG_ERROR([libfuse3 (>= 3.0) doesn't work properly for lowlevel api])])
> +    have_fuse="yes"
> +  ], [
> +    PKG_CHECK_MODULES([libfuse2], [fuse >= 2.6], [
> +      AC_DEFINE([FUSE_USE_VERSION], [26], [used FUSE API version])
> +      CPPFLAGS="${libfuse2_CFLAGS} ${CPPFLAGS}"
> +      LIBS="${libfuse2_LIBS} $LIBS"
> +      AC_CHECK_LIB(fuse, fuse_lowlevel_new, [], [
> +        AC_MSG_ERROR([libfuse (>= 2.6) doesn't work properly for lowlevel api])])
> +      have_fuse="yes"
> +    ], [have_fuse="no"])
> +  ])
>    LIBS="${saved_LIBS}"
>    CPPFLAGS="${saved_CPPFLAGS}"], [have_fuse="no"])
>  
> diff --git a/fuse/Makefile.am b/fuse/Makefile.am
> index 50be783..c63efcd 100644
> --- a/fuse/Makefile.am
> +++ b/fuse/Makefile.am
> @@ -5,6 +5,6 @@ noinst_HEADERS = $(top_srcdir)/fuse/macosx.h
>  bin_PROGRAMS     = erofsfuse
>  erofsfuse_SOURCES = main.c
>  erofsfuse_CFLAGS = -Wall -I$(top_srcdir)/include
> -erofsfuse_CFLAGS += -DFUSE_USE_VERSION=26 ${libfuse_CFLAGS} ${libselinux_CFLAGS}
> -erofsfuse_LDADD = $(top_builddir)/lib/liberofs.la ${libfuse_LIBS} ${liblz4_LIBS} \
> +erofsfuse_CFLAGS += ${libfuse2_CFLAGS} ${libfuse3_CFLAGS} ${libselinux_CFLAGS}
> +erofsfuse_LDADD = $(top_builddir)/lib/liberofs.la ${libfuse2_LIBS} ${libfuse3_LIBS} ${liblz4_LIBS} \
>  	${libselinux_LIBS} ${liblzma_LIBS} ${zlib_LIBS} ${libdeflate_LIBS}
> diff --git a/fuse/main.c b/fuse/main.c
> index 821d98c..c598870 100644
> --- a/fuse/main.c
> +++ b/fuse/main.c
> @@ -1,13 +1,12 @@
>  // SPDX-License-Identifier: GPL-2.0+
>  /*
>   * Created by Li Guifu <blucerlee at gmail.com>
> + * Lowlevel added by Li Yiyan <lyy0627 at sjtu.edu.cn>
>   */
>  #include <stdlib.h>
>  #include <string.h>
>  #include <signal.h>
>  #include <libgen.h>
> -#include <fuse.h>
> -#include <fuse_opt.h>
>  #include "macosx.h"
>  #include "erofs/config.h"
>  #include "erofs/print.h"
> @@ -15,177 +14,508 @@
>  #include "erofs/dir.h"
>  #include "erofs/inode.h"
>  
> -struct erofsfuse_dir_context {
> +#include <float.h>
> +#include <fuse.h>
> +#include <fuse_lowlevel.h>
> +
> +/* used in list/getxattr, given buf size is 0 and
> + * expected return val is xattr size
> + * FIXME: remove this workaround by new lib interface
> + */
> +#define EROFSFUSE_XATTR_BUF_SIZE 4096
> +#define EROFSFUSE_TIMEOUT DBL_MAX
> +
> +struct erofsfuse_readdir_context {
>  	struct erofs_dir_context ctx;
> -	fuse_fill_dir_t filler;
> -	struct fuse_file_info *fi;
> +
> +	fuse_req_t req;
>  	void *buf;
> +	int is_plus;
> +	size_t offset;
> +	size_t buf_size;
> +	size_t start_off;
> +	struct fuse_file_info *fi;
> +};
> +
> +struct erofsfuse_lookupdir_context {
> +	struct erofs_dir_context ctx;
> +
> +	const char *target_name;
> +	struct fuse_entry_param *ent;
>  };
>  
> -static int erofsfuse_fill_dentries(struct erofs_dir_context *ctx)
> +static int erofsfuse_add_dentry(struct erofs_dir_context *ctx)
>  {
> -	struct erofsfuse_dir_context *fusectx = (void *)ctx;
> -	struct stat st = {0};
> +	size_t r = 0;

size_t size = 0;

> +	struct stat st = { 0 };

move it under !->is_plus

>  	char dname[EROFS_NAME_LEN + 1];
> +	struct erofsfuse_readdir_context *readdir_ctx =
> +		(struct erofsfuse_readdir_context *)ctx;

let's continue to use void* as before.

> +
> +	if (readdir_ctx->offset < readdir_ctx->start_off) {
> +		readdir_ctx->offset +=
> +			ctx->de_namelen + sizeof(struct erofs_dirent);
> +		return 0;
> +	}
>  
>  	strncpy(dname, ctx->dname, ctx->de_namelen);
>  	dname[ctx->de_namelen] = '\0';
> -	st.st_mode = erofs_ftype_to_dtype(ctx->de_ftype) << 12;
> -	fusectx->filler(fusectx->buf, dname, &st, 0);
> +	readdir_ctx->offset += ctx->de_namelen + sizeof(struct erofs_dirent);
> +
> +	if (!readdir_ctx->is_plus) { /* fuse 3 still use non-plus readdir */
		struct stat st = { 0 };

> +		st.st_mode = erofs_ftype_to_dtype(ctx->de_ftype);
> +		st.st_ino = ctx->de_nid;
> +
> +		r = fuse_add_direntry(readdir_ctx->req, readdir_ctx->buf,
> +				      readdir_ctx->buf_size, dname, &st,
> +				      readdir_ctx->offset);
> +	} else {
> +#if FUSE_MAJOR_VERSION >= 3
> +		struct fuse_entry_param param;
> +
> +		param.ino = ctx->de_nid;
> +		param.generation = 0;
> +		param.attr.st_ino = ctx->de_nid;
> +		param.attr.st_mode = erofs_ftype_to_dtype(ctx->de_ftype);
> +		param.attr_timeout = param.entry_timeout = EROFSFUSE_TIMEOUT;
> +
> +		r = fuse_add_direntry_plus(readdir_ctx->req, readdir_ctx->buf,
> +					   readdir_ctx->buf_size, dname, &param,
> +					   readdir_ctx->offset);
> +#else
> +		erofs_err("fuse 2 readdirplus is not supported");
> +#endif
> +	}
> +
> +	if (r > readdir_ctx->buf_size) {
> +		readdir_ctx->offset -=
> +			ctx->de_namelen + sizeof(struct erofs_dirent);
> +		return 1;
> +	}
> +	readdir_ctx->buf += r;
> +	readdir_ctx->buf_size -= r;
>  	return 0;
>  }
>  
> -int erofsfuse_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
> -		      off_t offset, struct fuse_file_info *fi)
> +static void erofsfuse_fill_stat(struct erofs_inode *vi, struct stat *stbuf)
>  {
> -	int ret;
> -	struct erofs_inode dir;
> -	struct erofsfuse_dir_context ctx = {
> -		.ctx.dir = &dir,
> -		.ctx.cb = erofsfuse_fill_dentries,
> -		.filler = filler,
> -		.fi = fi,
> -		.buf = buf,
> -	};
> -	erofs_dbg("readdir:%s offset=%llu", path, (long long)offset);
> -
> -	dir.sbi = &sbi;
> -	ret = erofs_ilookup(path, &dir);
> -	if (ret)
> -		return ret;
> +	stbuf->st_mode = vi->i_mode;
> +	stbuf->st_nlink = vi->i_nlink;
>  
> -	erofs_dbg("path=%s nid = %llu", path, dir.nid | 0ULL);
> -	if (!S_ISDIR(dir.i_mode))
> -		return -ENOTDIR;
> +	if (!S_ISDIR(stbuf->st_mode))
> +		stbuf->st_size = vi->i_size;
> +	if (S_ISBLK(vi->i_mode) || S_ISCHR(vi->i_mode))
> +		stbuf->st_rdev = vi->u.i_rdev;
> +
> +	stbuf->st_blocks = roundup(vi->i_size, erofs_blksiz(&sbi)) >> 9;
> +
> +	stbuf->st_uid = vi->i_uid;
> +	stbuf->st_gid = vi->i_gid;
> +
> +	stbuf->st_ctime = vi->i_mtime;
> +	stbuf->st_mtime = stbuf->st_ctime;
> +	stbuf->st_atime = stbuf->st_ctime;
> +}
> +
> +static int erofsfuse_lookup_dentry(struct erofs_dir_context *ctx)
> +{
> +	int r = 0;
> +	struct erofs_inode vi = { .sbi = &sbi };
> +	struct erofsfuse_lookupdir_context *lookup_ctx =
> +		(struct erofsfuse_lookupdir_context *)ctx;
> +
> +	if (lookup_ctx->ent->ino == 0 &&
> +	    strlen(lookup_ctx->target_name) == ctx->de_namelen &&
> +	    !strncmp(lookup_ctx->target_name, ctx->dname, ctx->de_namelen)) {
> +		lookup_ctx->ent->ino = ctx->de_nid;
> +		lookup_ctx->ent->attr.st_ino = ctx->de_nid;
> +		vi.nid = (erofs_nid_t)ctx->de_nid;
> +
> +		r = erofs_read_inode_from_disk(&vi);
> +		if (r < 0)
> +			return r;
> +
> +		erofsfuse_fill_stat(&vi, &(lookup_ctx->ent->attr));
> +	}
> +
> +	return 0;
> +}

How about below?

{
	struct erofsfuse_lookupdir_context *lookup_ctx = (void *)ctx;

	if (lookup_ctx->ent->ino != 0 ||
	    strlen(lookup_ctx->target_name) != ctx->de_namelen)
		return 0;

	if (!strncmp(lookup_ctx->target_name, ctx->dname, ctx->de_namelen)) {
		int ret;
		struct erofs_inode vi = {
			.sbi = &sbi,
			.nid = (erofs_nid_t)ctx->de_nid,
		};

		ret = erofs_read_inode_from_disk(&vi);
		if (ret < 0)
			return ret;

		lookup_ctx->ent->ino = ctx->de_nid;
		lookup_ctx->ent->attr.st_ino = ctx->de_nid;

		erofsfuse_fill_stat(&vi, &(lookup_ctx->ent->attr));
	}
	return 0;
}

> +
> +static inline erofs_nid_t erofsfuse_getnid(fuse_ino_t ino)
> +{
> +	return ino == FUSE_ROOT_ID ? sbi.root_nid : (erofs_nid_t)ino;
> +}
> +
> +static inline void erofsfuse_readdir_general(fuse_req_t req, fuse_ino_t ino,
> +					     size_t size, off_t off,
> +					     struct fuse_file_info *fi,
> +					     int plus)
> +{
> +	int err = 0;
> +	char *buf = malloc(size);
> +	struct erofsfuse_readdir_context ctx;
> +	struct erofs_inode *vi = (struct erofs_inode *)fi->fh;
> +
> +	erofs_dbg("ino: %lu, size: %lu, off: %lu, plus: %d", ino, size, off,
> +		  plus);
> +	if (!buf) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +	ctx.ctx.dir = vi;
> +	ctx.ctx.cb = erofsfuse_add_dentry;
> +
> +	ctx.fi = fi;
> +	ctx.buf = buf;
> +	ctx.buf_size = size;
> +	ctx.req = req;
> +	ctx.offset = 0;
> +	ctx.start_off = off;
> +	ctx.is_plus = plus;
>  
> -	if (!dir.i_size)
> -		return 0;
>  #ifdef NDEBUG
> -	return erofs_iterate_dir(&ctx.ctx, false);
> +	err = erofs_iterate_dir(&ctx.ctx, false);
>  #else
> -	return erofs_iterate_dir(&ctx.ctx, true);
> +	err = erofs_iterate_dir(&ctx.ctx, true);
>  #endif
> +
> +	if (err < 0) /* if buffer insufficient, return 1 */
> +		fuse_reply_err(req, EIO);
> +	else
> +		fuse_reply_buf(req, buf, size - ctx.buf_size);
> +
> +	free(buf);
>  }
>  
> -static void *erofsfuse_init(struct fuse_conn_info *info)
> +static void erofsfuse_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
> +			      off_t off, struct fuse_file_info *fi)
>  {
> -	erofs_info("Using FUSE protocol %d.%d", info->proto_major, info->proto_minor);
> -	return NULL;
> +	erofsfuse_readdir_general(req, ino, size, off, fi, 0);
>  }
>  
> -static int erofsfuse_open(const char *path, struct fuse_file_info *fi)
> +#if FUSE_MAJOR_VERSION >= 3
> +static void erofsfuse_readdirplus(fuse_req_t req, fuse_ino_t ino, size_t size,
> +				  off_t off, struct fuse_file_info *fi)
>  {
> -	erofs_dbg("open path=%s", path);
> +	erofsfuse_readdir_general(req, ino, size, off, fi, 1);
> +}
> +#endif
>  
> -	if ((fi->flags & O_ACCMODE) != O_RDONLY)
> -		return -EACCES;
> +static void erofsfuse_init(void *userdata, struct fuse_conn_info *conn)
> +{
> +	erofs_info("Using FUSE protocol %d.%d", conn->proto_major,
> +		   conn->proto_minor);
> +}
>  
> -	return 0;
> +static void erofsfuse_open(fuse_req_t req, fuse_ino_t ino,
> +			   struct fuse_file_info *fi)
> +{
> +	int ret = 0;
> +	struct erofs_inode *vi;
> +
> +	erofs_dbg("ino = %lu", ino);

redundant logs?

> +	if (fi->flags & (O_WRONLY | O_RDWR)) {
> +		fuse_reply_err(req, EROFS);
> +		return;
> +	}
> +
> +	if (ino == FUSE_ROOT_ID) {
> +		fuse_reply_err(req, EISDIR);
> +		return;
> +	}
> +
> +	vi = (struct erofs_inode *)malloc(sizeof(struct erofs_inode));
> +	if (!vi) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +
> +	vi->sbi = &sbi;
> +	vi->nid = (erofs_nid_t)ino;
> +	ret = erofs_read_inode_from_disk(vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
> +
> +	if (!S_ISREG(vi->i_mode)) {
> +		fuse_reply_err(req, EISDIR);
> +	} else {
> +		fi->fh = (uint64_t)vi;
> +		fi->keep_cache = 1;
> +		fuse_reply_open(req, fi);
> +		return;
> +	}
> +
> +out:
> +	free(vi);
>  }
>  
> -static int erofsfuse_getattr(const char *path, struct stat *stbuf)
> +static void erofsfuse_getattr(fuse_req_t req, fuse_ino_t ino,
> +			      struct fuse_file_info *fi)
>  {
> -	struct erofs_inode vi = { .sbi = &sbi };
>  	int ret;
> +	struct stat stbuf = { 0 };
> +	struct erofs_inode vi = { .sbi = &sbi };

	struct erofs_inode vi = {
		.sbi = &sbi,
		.nid = erofsfuse_getnid(ino),
	};

>  
> -	erofs_dbg("getattr(%s)", path);
> -	ret = erofs_ilookup(path, &vi);
> -	if (ret)
> -		return -ENOENT;
> -
> -	stbuf->st_mode  = vi.i_mode;
> -	stbuf->st_nlink = vi.i_nlink;
> -	stbuf->st_size  = vi.i_size;
> -	stbuf->st_blocks = roundup(vi.i_size, erofs_blksiz(vi.sbi)) >> 9;
> -	stbuf->st_uid = vi.i_uid;
> -	stbuf->st_gid = vi.i_gid;
> -	if (S_ISBLK(vi.i_mode) || S_ISCHR(vi.i_mode))
> -		stbuf->st_rdev = vi.u.i_rdev;
> -	stbuf->st_ctime = vi.i_mtime;
> -	stbuf->st_mtime = stbuf->st_ctime;
> -	stbuf->st_atime = stbuf->st_ctime;
> -	return 0;
> +	erofs_dbg("ino: %lu", ino);
> +	vi.nid = erofsfuse_getnid(ino);
> +	ret = erofs_read_inode_from_disk(&vi);
> +	if (ret < 0)
> +		fuse_reply_err(req, ENOENT);
> +
> +	erofsfuse_fill_stat(&vi, &stbuf);
> +	stbuf.st_ino = ino;
> +
> +	fuse_reply_attr(req, &stbuf, EROFSFUSE_TIMEOUT);
>  }
>  
> -static int erofsfuse_read(const char *path, char *buffer,
> -			  size_t size, off_t offset,
> -			  struct fuse_file_info *fi)
> +static void erofsfuse_opendir(fuse_req_t req, fuse_ino_t ino,
> +			      struct fuse_file_info *fi)
>  {
>  	int ret;
> -	struct erofs_inode vi;
> +	struct erofs_inode *vi;
>  
> -	erofs_dbg("path:%s size=%zd offset=%llu", path, size, (long long)offset);
> +	erofs_dbg("ino: %lu", ino);
> +	vi = (struct erofs_inode *)malloc(sizeof(struct erofs_inode));
> +	if (!vi) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
>  
> -	vi.sbi = &sbi;
> -	ret = erofs_ilookup(path, &vi);
> -	if (ret)
> -		return ret;
> +	vi->sbi = &sbi;
> +	vi->nid = erofsfuse_getnid(ino);
> +	ret = erofs_read_inode_from_disk(vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
>  
> -	ret = erofs_pread(&vi, buffer, size, offset);
> -	if (ret)
> -		return ret;
> -	if (offset >= vi.i_size)
> -		return 0;
> -	if (offset + size > vi.i_size)
> -		return vi.i_size - offset;
> -	return size;
> +	if (!S_ISDIR(vi->i_mode)) {
> +		fuse_reply_err(req, ENOTDIR);
> +		goto out;
> +	}
> +
> +	fi->fh = (uint64_t)vi;
> +	fuse_reply_open(req, fi);
> +	return;
> +
> +out:
> +	free(vi);
>  }
>  
> -static int erofsfuse_readlink(const char *path, char *buffer, size_t size)
> +static void erofsfuse_release(fuse_req_t req, fuse_ino_t ino,
> +			      struct fuse_file_info *fi)
>  {
> -	int ret = erofsfuse_read(path, buffer, size, 0, NULL);
> -
> -	if (ret < 0)
> -		return ret;
> -	DBG_BUGON(ret > size);
> -	if (ret == size)
> -		buffer[size - 1] = '\0';
> -	erofs_dbg("readlink(%s): %s", path, buffer);
> -	return 0;
> +	free((struct erofs_inode *)fi->fh);
> +	fi->fh = 0;
> +	fuse_reply_err(req, 0);
>  }
>  
> -static int erofsfuse_getxattr(const char *path, const char *name, char *value,
> -			size_t size
> -#ifdef __APPLE__
> -			, uint32_t position)
> +static void erofsfuse_lookup(fuse_req_t req, fuse_ino_t parent,
> +			     const char *name)
> +{
> +	int err, ret;

no need `err`, just use `ret`

> +	struct erofs_inode *vi;
> +	struct fuse_entry_param fentry;
> +	struct erofsfuse_lookupdir_context ctx;
> +
> +	vi = (struct erofs_inode *)malloc(sizeof(struct erofs_inode));
> +	if (!vi) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +
> +	vi->sbi = &sbi;
> +	vi->nid = erofsfuse_getnid(parent);
> +	ret = erofs_read_inode_from_disk(vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
> +	if (!S_ISDIR(vi->i_mode)) {
> +		fuse_reply_err(req, ENOTDIR);
> +		goto out;
> +	}
> +
> +	memset(&fentry, 0, sizeof(fentry));
> +	fentry.ino = 0;
> +	fentry.attr_timeout = fentry.entry_timeout = EROFSFUSE_TIMEOUT;
> +	ctx.ctx.dir = vi;
> +	ctx.ctx.cb = erofsfuse_lookup_dentry;
> +
> +	ctx.ent = &fentry;
> +	ctx.target_name = name;
> +
> +#ifdef NDEBUG
> +	err = erofs_iterate_dir(&ctx.ctx, false);
>  #else
> -			)
> +	err = erofs_iterate_dir(&ctx.ctx, true);
>  #endif
> +
> +	if (err < 0) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
> +	fuse_reply_entry(req, &fentry);
> +
> +out:
> +	free(vi);
> +}
> +
> +static void erofsfuse_read(fuse_req_t req, fuse_ino_t ino, size_t size,
> +			   off_t off, struct fuse_file_info *fi)
>  {
>  	int ret;
> -	struct erofs_inode vi;
> +	struct erofs_inode *vi = (struct erofs_inode *)fi->fh;
> +	char *buf;
>  
> -	erofs_dbg("getxattr(%s): name=%s size=%llu", path, name, size);
> +	erofs_dbg("ino = %lu, size = %lu, off = %lu", ino, size, off);
> +	if (!S_ISREG(vi->i_mode)) {
> +		fuse_reply_err(req, EIO);
> +		return;
> +	}
>  
> -	vi.sbi = &sbi;
> -	ret = erofs_ilookup(path, &vi);
> -	if (ret)
> -		return ret;
> +	buf = malloc(size);
> +	if (!buf) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +
> +	ret = erofs_pread(vi, buf, size, off);
> +	if (ret) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
> +	if (off >= vi->i_size)
> +		ret = 0;
> +	else if (off + size > vi->i_size)
> +		ret = vi->i_size - off;
> +	else
> +		ret = size;
> +
> +	fuse_reply_buf(req, buf, ret);
>  
> -	return erofs_getxattr(&vi, name, value, size);
> +out:
> +	free(buf);
>  }
>  
> -static int erofsfuse_listxattr(const char *path, char *list, size_t size)
> +static void erofsfuse_readlink(fuse_req_t req, fuse_ino_t ino)
>  {
>  	int ret;
> -	struct erofs_inode vi;
> +	char *dst;
> +	struct erofs_inode vi = { .sbi = &sbi };

	struct erofs_inode vi = {
		.sbi = &sbi,
		.nid = erofsfuse_getnid(ino),
	};

> +
> +	erofs_dbg("ino = %lu", ino);
> +	vi.nid = erofsfuse_getnid(ino);
> +	ret = erofs_read_inode_from_disk(&vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		return;
> +	}
>  
> -	erofs_dbg("listxattr(%s): size=%llu", path, size);
> +	if (!S_ISLNK(vi.i_mode)) {
> +		fuse_reply_err(req, EINVAL);
> +		return;
> +	}
>  
> -	vi.sbi = &sbi;
> -	ret = erofs_ilookup(path, &vi);
> -	if (ret)
> -		return ret;
> +	dst = malloc(vi.i_size + 1);
> +	if (!dst) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
>  
> -	return erofs_listxattr(&vi, list, size);
> +	ret = erofs_pread(&vi, dst, vi.i_size, 0);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		goto out;
> +	}
> +
> +	dst[vi.i_size] = '\0';
> +	fuse_reply_readlink(req, dst);
> +
> +out:
> +	free(dst);
> +}
> +
> +static void erofsfuse_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,
> +			       size_t size)
> +{
> +	int ret;
> +	char *buf = NULL;
> +	struct erofs_inode vi = { .sbi = &sbi };
> +	size_t real = size == 0 ? EROFSFUSE_XATTR_BUF_SIZE : size;

	struct erofs_inode vi = {
		.sbi = &sbi,
		.nid = erofsfuse_getnid(ino),
	};
	char *buf;
	size_t bufsize = size;

> +
> +	erofs_dbg("ino = %lu, name = %s, size = %lu", ino, name, size);

It's better to leave a blank line after this debug code.

> +	vi.nid = erofsfuse_getnid(ino);
> +	ret = erofs_read_inode_from_disk(&vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		return;
> +	}
> +
> +	buf = malloc(real);

	if (bufsize == 0)
		bufsize = EROFSFUSE_XATTR_BUF_SIZE;
	buf = malloc(bufsize);

> +	if (!buf) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +
> +	ret = erofs_getxattr(&vi, name, buf, real);
> +	if (ret < 0)
> +		fuse_reply_err(req, -ret);
> +	else if (size == 0)
> +		fuse_reply_xattr(req, ret);
> +	else
> +		fuse_reply_buf(req, buf, ret);
> +
> +	free(buf);
>  }
>  
> -static struct fuse_operations erofs_ops = {
> +static void erofsfuse_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)
> +{
> +	int ret;
> +	char *buf = NULL;
> +	struct erofs_inode vi = { .sbi = &sbi };
> +	size_t real = size == 0 ? EROFSFUSE_XATTR_BUF_SIZE : size;
> +
> +	erofs_dbg("ino = %lu, size = %lu", ino, size);
> +	vi.nid = erofsfuse_getnid(ino);
> +	ret = erofs_read_inode_from_disk(&vi);
> +	if (ret < 0) {
> +		fuse_reply_err(req, EIO);
> +		return;
> +	}
> +
> +	buf = malloc(real);

ditto

> +	if (!buf) {
> +		fuse_reply_err(req, ENOMEM);
> +		return;
> +	}
> +
> +	ret = erofs_listxattr(&vi, buf, real);
> +	if (ret < 0)
> +		fuse_reply_err(req, -ret);
> +	else if (size == 0)
> +		fuse_reply_xattr(req, ret);
> +	else
> +		fuse_reply_buf(req, buf, ret);
> +
> +	free(buf);
> +}
> +
> +static struct fuse_lowlevel_ops erofsfuse_lops = {
>  	.getxattr = erofsfuse_getxattr,
> +	.opendir = erofsfuse_opendir,
> +	.releasedir = erofsfuse_release,
> +	.release = erofsfuse_release,
> +	.lookup = erofsfuse_lookup,
>  	.listxattr = erofsfuse_listxattr,
>  	.readlink = erofsfuse_readlink,
>  	.getattr = erofsfuse_getattr,
>  	.readdir = erofsfuse_readdir,
> +#if FUSE_MAJOR_VERSION >= 3
> +	.readdirplus = erofsfuse_readdirplus,
> +#endif
>  	.open = erofsfuse_open,
>  	.read = erofsfuse_read,
>  	.init = erofsfuse_init,
> @@ -200,18 +530,20 @@ static struct options {
>  	bool odebug;
>  } fusecfg;
>  
> -#define OPTION(t, p) { t, offsetof(struct options, p), 1 }
> +#define OPTION(t, p)                              \
> +	{                                         \
> +		t, offsetof(struct options, p), 1 \
> +	}

keep it as it's

>  static const struct fuse_opt option_spec[] = {
> -	OPTION("--offset=%lu", offset),
> -	OPTION("--dbglevel=%u", debug_lvl),
> -	OPTION("--help", show_help),
> -	FUSE_OPT_KEY("--device=", 1),
> -	FUSE_OPT_END
> +	OPTION("--offset=%lu", offset), OPTION("--dbglevel=%u", debug_lvl),
> +	OPTION("--help", show_help), FUSE_OPT_KEY("--device=", 1), FUSE_OPT_END

ditto

>  };
>  
>  static void usage(void)
>  {
> +#if FUSE_MAJOR_VERSION < 3
>  	struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
> +#endif
>  
>  	fputs("usage: [options] IMAGE MOUNTPOINT\n\n"
>  	      "Options:\n"
> @@ -221,7 +553,8 @@ static void usage(void)
>  #if FUSE_MAJOR_VERSION < 3
>  	      "    --help                 display this help and exit\n"
>  #endif
> -	      "\n", stderr);
> +	      "\n",
> +	      stderr);

ditto

>  
>  #if FUSE_MAJOR_VERSION >= 3
>  	fuse_cmdline_help();
> @@ -261,8 +594,10 @@ static int optional_opt_func(void *data, const char *arg, int key,
>  			fusecfg.disk = strdup(arg);
>  			return 0;
>  		}
> -		if (!fusecfg.mountpoint)
> +		if (!fusecfg.mountpoint) {
>  			fusecfg.mountpoint = strdup(arg);
> +			return 0;
> +		}
>  	case FUSE_OPT_KEY_OPT:
>  		if (!strcmp(arg, "-d"))
>  			fusecfg.odebug = true;
> @@ -301,10 +636,11 @@ static void signal_handle_sigsegv(int signal)
>  int main(int argc, char *argv[])
>  {
>  	int ret;
> +	struct fuse_session *se;
>  	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
>  
>  	erofs_init_configure();
> -	printf("%s %s\n", basename(argv[0]), cfg.c_version);
> +	erofs_dbg("%s %s", basename(argv[0]), cfg.c_version);
>  
>  #if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE)
>  	if (signal(SIGSEGV, signal_handle_sigsegv) == SIG_ERR) {
> @@ -341,7 +677,38 @@ int main(int argc, char *argv[])
>  		goto err_dev_close;
>  	}
>  
> -	ret = fuse_main(args.argc, args.argv, &erofs_ops, NULL);
> +#if FUSE_MAJOR_VERSION >= 3
> +	se = fuse_session_new(&args, &erofsfuse_lops, sizeof(erofsfuse_lops),
> +			      NULL);
> +	if (se != NULL) {
> +		fuse_set_signal_handlers(se);
> +		fuse_session_mount(se, fusecfg.mountpoint);
> +
> +		ret = fuse_session_loop(se);
> +
> +		fuse_remove_signal_handlers(se);
> +		fuse_session_unmount(se);
> +		fuse_session_destroy(se);
> +	}
> +#else
> +	struct fuse_chan *ch;

avoid this declaration here

> +
> +	ch = fuse_mount(fusecfg.mountpoint, &args);
> +	if (ch != NULL) {
> +		se = fuse_lowlevel_new(&args, &erofsfuse_lops,
> +				       sizeof(erofsfuse_lops), NULL);
> +		if (se != NULL) {
> +			if (fuse_set_signal_handlers(se) != -1) {
> +				fuse_session_add_chan(se, ch);
> +				ret = fuse_session_loop(se);
> +				fuse_remove_signal_handlers(se);
> +				fuse_session_remove_chan(ch);
> +			}
> +			fuse_session_destroy(se);
> +		}
> +		fuse_unmount(fusecfg.mountpoint, ch);
> +	}
> +#endif
>  
>  	erofs_put_super(&sbi);
>  err_dev_close:



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