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qemu-e2k/block/export/fuse.c

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/*
* Present a block device as a raw image through FUSE
*
* Copyright (c) 2020 Max Reitz <mreitz@redhat.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; under version 2 or later of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#define FUSE_USE_VERSION 31
#include "qemu/osdep.h"
#include "block/aio.h"
#include "block/block.h"
#include "block/export.h"
#include "block/fuse.h"
#include "block/qapi.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-block.h"
#include "sysemu/block-backend.h"
#include <fuse.h>
#include <fuse_lowlevel.h>
/* Prevent overly long bounce buffer allocations */
#define FUSE_MAX_BOUNCE_BYTES (MIN(BDRV_REQUEST_MAX_BYTES, 64 * 1024 * 1024))
typedef struct FuseExport {
BlockExport common;
struct fuse_session *fuse_session;
struct fuse_buf fuse_buf;
bool mounted, fd_handler_set_up;
char *mountpoint;
bool writable;
bool growable;
/* Whether allow_other was used as a mount option or not */
bool allow_other;
mode_t st_mode;
uid_t st_uid;
gid_t st_gid;
} FuseExport;
static GHashTable *exports;
static const struct fuse_lowlevel_ops fuse_ops;
static void fuse_export_shutdown(BlockExport *exp);
static void fuse_export_delete(BlockExport *exp);
static void init_exports_table(void);
static int setup_fuse_export(FuseExport *exp, const char *mountpoint,
bool allow_other, Error **errp);
static void read_from_fuse_export(void *opaque);
static bool is_regular_file(const char *path, Error **errp);
static int fuse_export_create(BlockExport *blk_exp,
BlockExportOptions *blk_exp_args,
Error **errp)
{
FuseExport *exp = container_of(blk_exp, FuseExport, common);
BlockExportOptionsFuse *args = &blk_exp_args->u.fuse;
int ret;
assert(blk_exp_args->type == BLOCK_EXPORT_TYPE_FUSE);
/* For growable exports, take the RESIZE permission */
if (args->growable) {
uint64_t blk_perm, blk_shared_perm;
blk_get_perm(exp->common.blk, &blk_perm, &blk_shared_perm);
ret = blk_set_perm(exp->common.blk, blk_perm | BLK_PERM_RESIZE,
blk_shared_perm, errp);
if (ret < 0) {
return ret;
}
}
init_exports_table();
/*
* It is important to do this check before calling is_regular_file() --
* that function will do a stat(), which we would have to handle if we
* already exported something on @mountpoint. But we cannot, because
* we are currently caught up here.
* (Note that ideally we would want to resolve relative paths here,
* but bdrv_make_absolute_filename() might do the wrong thing for
* paths that contain colons, and realpath() would resolve symlinks,
* which we do not want: The mount point is not going to be the
* symlink's destination, but the link itself.)
* So this will not catch all potential clashes, but hopefully at
* least the most common one of specifying exactly the same path
* string twice.
*/
if (g_hash_table_contains(exports, args->mountpoint)) {
error_setg(errp, "There already is a FUSE export on '%s'",
args->mountpoint);
ret = -EEXIST;
goto fail;
}
if (!is_regular_file(args->mountpoint, errp)) {
ret = -EINVAL;
goto fail;
}
exp->mountpoint = g_strdup(args->mountpoint);
exp->writable = blk_exp_args->writable;
exp->growable = args->growable;
/* set default */
if (!args->has_allow_other) {
args->allow_other = FUSE_EXPORT_ALLOW_OTHER_AUTO;
}
exp->st_mode = S_IFREG | S_IRUSR;
if (exp->writable) {
exp->st_mode |= S_IWUSR;
}
exp->st_uid = getuid();
exp->st_gid = getgid();
if (args->allow_other == FUSE_EXPORT_ALLOW_OTHER_AUTO) {
/* Ignore errors on our first attempt */
ret = setup_fuse_export(exp, args->mountpoint, true, NULL);
exp->allow_other = ret == 0;
if (ret < 0) {
ret = setup_fuse_export(exp, args->mountpoint, false, errp);
}
} else {
exp->allow_other = args->allow_other == FUSE_EXPORT_ALLOW_OTHER_ON;
ret = setup_fuse_export(exp, args->mountpoint, exp->allow_other, errp);
}
if (ret < 0) {
goto fail;
}
return 0;
fail:
fuse_export_delete(blk_exp);
return ret;
}
/**
* Allocates the global @exports hash table.
*/
static void init_exports_table(void)
{
if (exports) {
return;
}
exports = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
}
/**
* Create exp->fuse_session and mount it.
*/
static int setup_fuse_export(FuseExport *exp, const char *mountpoint,
bool allow_other, Error **errp)
{
const char *fuse_argv[4];
char *mount_opts;
struct fuse_args fuse_args;
int ret;
/*
* max_read needs to match what fuse_init() sets.
* max_write need not be supplied.
*/
mount_opts = g_strdup_printf("max_read=%zu,default_permissions%s",
FUSE_MAX_BOUNCE_BYTES,
allow_other ? ",allow_other" : "");
fuse_argv[0] = ""; /* Dummy program name */
fuse_argv[1] = "-o";
fuse_argv[2] = mount_opts;
fuse_argv[3] = NULL;
fuse_args = (struct fuse_args)FUSE_ARGS_INIT(3, (char **)fuse_argv);
exp->fuse_session = fuse_session_new(&fuse_args, &fuse_ops,
sizeof(fuse_ops), exp);
g_free(mount_opts);
if (!exp->fuse_session) {
error_setg(errp, "Failed to set up FUSE session");
ret = -EIO;
goto fail;
}
ret = fuse_session_mount(exp->fuse_session, mountpoint);
if (ret < 0) {
error_setg(errp, "Failed to mount FUSE session to export");
ret = -EIO;
goto fail;
}
exp->mounted = true;
g_hash_table_insert(exports, g_strdup(mountpoint), NULL);
aio_set_fd_handler(exp->common.ctx,
fuse_session_fd(exp->fuse_session), true,
read_from_fuse_export, NULL, NULL, exp);
exp->fd_handler_set_up = true;
return 0;
fail:
fuse_export_shutdown(&exp->common);
return ret;
}
/**
* Callback to be invoked when the FUSE session FD can be read from.
* (This is basically the FUSE event loop.)
*/
static void read_from_fuse_export(void *opaque)
{
FuseExport *exp = opaque;
int ret;
blk_exp_ref(&exp->common);
do {
ret = fuse_session_receive_buf(exp->fuse_session, &exp->fuse_buf);
} while (ret == -EINTR);
if (ret < 0) {
goto out;
}
fuse_session_process_buf(exp->fuse_session, &exp->fuse_buf);
out:
blk_exp_unref(&exp->common);
}
static void fuse_export_shutdown(BlockExport *blk_exp)
{
FuseExport *exp = container_of(blk_exp, FuseExport, common);
if (exp->fuse_session) {
fuse_session_exit(exp->fuse_session);
if (exp->fd_handler_set_up) {
aio_set_fd_handler(exp->common.ctx,
fuse_session_fd(exp->fuse_session), true,
NULL, NULL, NULL, NULL);
exp->fd_handler_set_up = false;
}
}
if (exp->mountpoint) {
/*
* Safe to drop now, because we will not handle any requests
* for this export anymore anyway.
*/
g_hash_table_remove(exports, exp->mountpoint);
}
}
static void fuse_export_delete(BlockExport *blk_exp)
{
FuseExport *exp = container_of(blk_exp, FuseExport, common);
if (exp->fuse_session) {
if (exp->mounted) {
fuse_session_unmount(exp->fuse_session);
}
fuse_session_destroy(exp->fuse_session);
}
free(exp->fuse_buf.mem);
g_free(exp->mountpoint);
}
/**
* Check whether @path points to a regular file. If not, put an
* appropriate message into *errp.
*/
static bool is_regular_file(const char *path, Error **errp)
{
struct stat statbuf;
int ret;
ret = stat(path, &statbuf);
if (ret < 0) {
error_setg_errno(errp, errno, "Failed to stat '%s'", path);
return false;
}
if (!S_ISREG(statbuf.st_mode)) {
error_setg(errp, "'%s' is not a regular file", path);
return false;
}
return true;
}
/**
* A chance to set change some parameters supplied to FUSE_INIT.
*/
static void fuse_init(void *userdata, struct fuse_conn_info *conn)
{
/*
* MIN_NON_ZERO() would not be wrong here, but what we set here
* must equal what has been passed to fuse_session_new().
* Therefore, as long as max_read must be passed as a mount option
* (which libfuse claims will be changed at some point), we have
* to set max_read to a fixed value here.
*/
conn->max_read = FUSE_MAX_BOUNCE_BYTES;
conn->max_write = MIN_NON_ZERO(BDRV_REQUEST_MAX_BYTES, conn->max_write);
}
/**
* Let clients look up files. Always return ENOENT because we only
* care about the mountpoint itself.
*/
static void fuse_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
{
fuse_reply_err(req, ENOENT);
}
/**
* Let clients get file attributes (i.e., stat() the file).
*/
static void fuse_getattr(fuse_req_t req, fuse_ino_t inode,
struct fuse_file_info *fi)
{
struct stat statbuf;
int64_t length, allocated_blocks;
time_t now = time(NULL);
FuseExport *exp = fuse_req_userdata(req);
length = blk_getlength(exp->common.blk);
if (length < 0) {
fuse_reply_err(req, -length);
return;
}
allocated_blocks = bdrv_get_allocated_file_size(blk_bs(exp->common.blk));
if (allocated_blocks <= 0) {
allocated_blocks = DIV_ROUND_UP(length, 512);
} else {
allocated_blocks = DIV_ROUND_UP(allocated_blocks, 512);
}
statbuf = (struct stat) {
.st_ino = inode,
.st_mode = exp->st_mode,
.st_nlink = 1,
.st_uid = exp->st_uid,
.st_gid = exp->st_gid,
.st_size = length,
.st_blksize = blk_bs(exp->common.blk)->bl.request_alignment,
.st_blocks = allocated_blocks,
.st_atime = now,
.st_mtime = now,
.st_ctime = now,
};
fuse_reply_attr(req, &statbuf, 1.);
}
static int fuse_do_truncate(const FuseExport *exp, int64_t size,
bool req_zero_write, PreallocMode prealloc)
{
uint64_t blk_perm, blk_shared_perm;
BdrvRequestFlags truncate_flags = 0;
int ret;
if (req_zero_write) {
truncate_flags |= BDRV_REQ_ZERO_WRITE;
}
/* Growable exports have a permanent RESIZE permission */
if (!exp->growable) {
blk_get_perm(exp->common.blk, &blk_perm, &blk_shared_perm);
ret = blk_set_perm(exp->common.blk, blk_perm | BLK_PERM_RESIZE,
blk_shared_perm, NULL);
if (ret < 0) {
return ret;
}
}
ret = blk_truncate(exp->common.blk, size, true, prealloc,
truncate_flags, NULL);
if (!exp->growable) {
/* Must succeed, because we are only giving up the RESIZE permission */
blk_set_perm(exp->common.blk, blk_perm, blk_shared_perm, &error_abort);
}
return ret;
}
/**
* Let clients set file attributes. Only resizing and changing
* permissions (st_mode, st_uid, st_gid) is allowed.
* Changing permissions is only allowed as far as it will actually
* permit access: Read-only exports cannot be given +w, and exports
* without allow_other cannot be given a different UID or GID, and
* they cannot be given non-owner access.
*/
static void fuse_setattr(fuse_req_t req, fuse_ino_t inode, struct stat *statbuf,
int to_set, struct fuse_file_info *fi)
{
FuseExport *exp = fuse_req_userdata(req);
int supported_attrs;
int ret;
supported_attrs = FUSE_SET_ATTR_SIZE | FUSE_SET_ATTR_MODE;
if (exp->allow_other) {
supported_attrs |= FUSE_SET_ATTR_UID | FUSE_SET_ATTR_GID;
}
if (to_set & ~supported_attrs) {
fuse_reply_err(req, ENOTSUP);
return;
}
/* Do some argument checks first before committing to anything */
if (to_set & FUSE_SET_ATTR_MODE) {
/*
* Without allow_other, non-owners can never access the export, so do
* not allow setting permissions for them
*/
if (!exp->allow_other &&
(statbuf->st_mode & (S_IRWXG | S_IRWXO)) != 0)
{
fuse_reply_err(req, EPERM);
return;
}
/* +w for read-only exports makes no sense, disallow it */
if (!exp->writable &&
(statbuf->st_mode & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
{
fuse_reply_err(req, EROFS);
return;
}
}
if (to_set & FUSE_SET_ATTR_SIZE) {
if (!exp->writable) {
fuse_reply_err(req, EACCES);
return;
}
ret = fuse_do_truncate(exp, statbuf->st_size, true, PREALLOC_MODE_OFF);
if (ret < 0) {
fuse_reply_err(req, -ret);
return;
}
}
if (to_set & FUSE_SET_ATTR_MODE) {
/* Ignore FUSE-supplied file type, only change the mode */
exp->st_mode = (statbuf->st_mode & 07777) | S_IFREG;
}
if (to_set & FUSE_SET_ATTR_UID) {
exp->st_uid = statbuf->st_uid;
}
if (to_set & FUSE_SET_ATTR_GID) {
exp->st_gid = statbuf->st_gid;
}
fuse_getattr(req, inode, fi);
}
/**
* Let clients open a file (i.e., the exported image).
*/
static void fuse_open(fuse_req_t req, fuse_ino_t inode,
struct fuse_file_info *fi)
{
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)
{
FuseExport *exp = fuse_req_userdata(req);
int64_t length;
void *buf;
int ret;
/* Limited by max_read, should not happen */
if (size > FUSE_MAX_BOUNCE_BYTES) {
fuse_reply_err(req, EINVAL);
return;
}
/**
* 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;
}
if (offset + size > length) {
size = length - offset;
}
buf = qemu_try_blockalign(blk_bs(exp->common.blk), size);
if (!buf) {
fuse_reply_err(req, ENOMEM);
return;
}
ret = blk_pread(exp->common.blk, offset, buf, size);
if (ret >= 0) {
fuse_reply_buf(req, buf, size);
} else {
fuse_reply_err(req, -ret);
}
qemu_vfree(buf);
}
/**
* 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);
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 (!exp->writable) {
fuse_reply_err(req, EACCES);
return;
}
/**
* 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;
}
if (offset + size > length) {
if (exp->growable) {
ret = fuse_do_truncate(exp, offset + size, true, PREALLOC_MODE_OFF);
if (ret < 0) {
fuse_reply_err(req, -ret);
return;
}
} else {
size = length - offset;
}
}
ret = blk_pwrite(exp->common.blk, offset, buf, size, 0);
if (ret >= 0) {
fuse_reply_write(req, size);
} else {
fuse_reply_err(req, -ret);
}
}
/**
* Let clients perform various fallocate() operations.
*/
static void fuse_fallocate(fuse_req_t req, fuse_ino_t inode, int mode,
off_t offset, off_t length,
struct fuse_file_info *fi)
{
FuseExport *exp = fuse_req_userdata(req);
int64_t blk_len;
int ret;
if (!exp->writable) {
fuse_reply_err(req, EACCES);
return;
}
blk_len = blk_getlength(exp->common.blk);
if (blk_len < 0) {
fuse_reply_err(req, -blk_len);
return;
}
if (mode & FALLOC_FL_KEEP_SIZE) {
length = MIN(length, blk_len - offset);
}
if (mode & FALLOC_FL_PUNCH_HOLE) {
if (!(mode & FALLOC_FL_KEEP_SIZE)) {
fuse_reply_err(req, EINVAL);
return;
}
do {
int size = MIN(length, BDRV_REQUEST_MAX_BYTES);
ret = blk_pdiscard(exp->common.blk, offset, size);
offset += size;
length -= size;
} while (ret == 0 && length > 0);
}
#ifdef CONFIG_FALLOCATE_ZERO_RANGE
else if (mode & FALLOC_FL_ZERO_RANGE) {
if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + length > blk_len) {
/* No need for zeroes, we are going to write them ourselves */
ret = fuse_do_truncate(exp, offset + length, false,
PREALLOC_MODE_OFF);
if (ret < 0) {
fuse_reply_err(req, -ret);
return;
}
}
do {
int size = MIN(length, BDRV_REQUEST_MAX_BYTES);
ret = blk_pwrite_zeroes(exp->common.blk,
offset, size, 0);
offset += size;
length -= size;
} while (ret == 0 && length > 0);
}
#endif /* CONFIG_FALLOCATE_ZERO_RANGE */
else if (!mode) {
/* We can only fallocate at the EOF with a truncate */
if (offset < blk_len) {
fuse_reply_err(req, EOPNOTSUPP);
return;
}
if (offset > blk_len) {
/* No preallocation needed here */
ret = fuse_do_truncate(exp, offset, true, PREALLOC_MODE_OFF);
if (ret < 0) {
fuse_reply_err(req, -ret);
return;
}
}
ret = fuse_do_truncate(exp, offset + length, true,
PREALLOC_MODE_FALLOC);
} else {
ret = -EOPNOTSUPP;
}
fuse_reply_err(req, ret < 0 ? -ret : 0);
}
/**
* Let clients fsync the exported image.
*/
static void fuse_fsync(fuse_req_t req, fuse_ino_t inode, int datasync,
struct fuse_file_info *fi)
{
FuseExport *exp = fuse_req_userdata(req);
int ret;
ret = blk_flush(exp->common.blk);
fuse_reply_err(req, ret < 0 ? -ret : 0);
}
/**
* Called before an FD to the exported image is closed. (libfuse
* notes this to be a way to return last-minute errors.)
*/
static void fuse_flush(fuse_req_t req, fuse_ino_t inode,
struct fuse_file_info *fi)
{
fuse_fsync(req, inode, 1, fi);
}
#ifdef CONFIG_FUSE_LSEEK
/**
* Let clients inquire allocation status.
*/
static void fuse_lseek(fuse_req_t req, fuse_ino_t inode, off_t offset,
int whence, struct fuse_file_info *fi)
{
FuseExport *exp = fuse_req_userdata(req);
if (whence != SEEK_HOLE && whence != SEEK_DATA) {
fuse_reply_err(req, EINVAL);
return;
}
while (true) {
int64_t pnum;
int ret;
ret = bdrv_block_status_above(blk_bs(exp->common.blk), NULL,
offset, INT64_MAX, &pnum, NULL, NULL);
if (ret < 0) {
fuse_reply_err(req, -ret);
return;
}
if (!pnum && (ret & BDRV_BLOCK_EOF)) {
int64_t blk_len;
/*
* If blk_getlength() rounds (e.g. by sectors), then the
* export length will be rounded, too. However,
* bdrv_block_status_above() may return EOF at unaligned
* offsets. We must not let this become visible and thus
* always simulate a hole between @offset (the real EOF)
* and @blk_len (the client-visible EOF).
*/
blk_len = blk_getlength(exp->common.blk);
if (blk_len < 0) {
fuse_reply_err(req, -blk_len);
return;
}
if (offset > blk_len || whence == SEEK_DATA) {
fuse_reply_err(req, ENXIO);
} else {
fuse_reply_lseek(req, offset);
}
return;
}
if (ret & BDRV_BLOCK_DATA) {
if (whence == SEEK_DATA) {
fuse_reply_lseek(req, offset);
return;
}
} else {
if (whence == SEEK_HOLE) {
fuse_reply_lseek(req, offset);
return;
}
}
/* Safety check against infinite loops */
if (!pnum) {
fuse_reply_err(req, ENXIO);
return;
}
offset += pnum;
}
}
#endif
static const struct fuse_lowlevel_ops fuse_ops = {
.init = fuse_init,
.lookup = fuse_lookup,
.getattr = fuse_getattr,
.setattr = fuse_setattr,
.open = fuse_open,
.read = fuse_read,
.write = fuse_write,
.fallocate = fuse_fallocate,
.flush = fuse_flush,
.fsync = fuse_fsync,
#ifdef CONFIG_FUSE_LSEEK
.lseek = fuse_lseek,
#endif
};
const BlockExportDriver blk_exp_fuse = {
.type = BLOCK_EXPORT_TYPE_FUSE,
.instance_size = sizeof(FuseExport),
.create = fuse_export_create,
.delete = fuse_export_delete,
.request_shutdown = fuse_export_shutdown,
};
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