diff options
Diffstat (limited to 'block/export/fuse.c')
| -rw-r--r-- | block/export/fuse.c | 812 |
1 files changed, 812 insertions, 0 deletions
diff --git a/block/export/fuse.c b/block/export/fuse.c new file mode 100644 index 000000000..823c126d2 --- /dev/null +++ b/block/export/fuse.c @@ -0,0 +1,812 @@ +/* + * 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> + +#if defined(CONFIG_FALLOCATE_ZERO_RANGE) +#include <linux/falloc.h> +#endif + +#ifdef __linux__ +#include <linux/fs.h> +#endif + +/* 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, +}; |