Daan De MeyerandLuca Boccassi
3978b076af
663f0bf5cb stopped reusing the original block device fd whenever partition scanning was requested (LO_FLAGS_PARTSCAN) but couldn't be enabled on the device, so that nested partition tables on devices the kernel won't scan (e.g. the pmOS/android case) get exposed via a real loop device. However that also forced a pointless loop device for any partition that carries a file system directly, e.g. a btrfs subvolume mounted via MountImages=. For multi-device btrfs this is fatal: the kernel rejects seeing the same member via both the original partition and the loop device, and the mount fails. A loop device is only ever needed here to expose a nested partition table. So only refuse the shortcut when the device actually carries one, probed via gpt_probe(), instead of whenever partition scanning is disabled. Devices carrying a file system directly (or nothing) take the shortcut as before. Add an integration test to cover the failure scenario of the original issue. Fixes: https://github.com/systemd/systemd/issues/42520 Replaces: https://github.com/systemd/systemd/pull/42576 Follow-up for 663f0bf5cb79ecaf6dd71441ecdc9dc401e7eae6 Co-Authored-By: Luca Boccassi <luca.boccassi@gmail.com> Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
64 lines
3.5 KiB
C
64 lines
3.5 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#pragma once
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#include "shared-forward.h"
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/* Some helpers for setting up loopback block devices */
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typedef struct LoopDevice {
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unsigned n_ref;
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int fd;
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int lock_fd;
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int nr; /* The loopback device index (i.e. 4 for /dev/loop4); if this object encapsulates a non-loopback block device, set to -1 */
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dev_t devno; /* The loopback device's own dev_t */
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char *node;
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sd_device *dev;
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char *backing_file;
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bool relinquished;
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bool created; /* If we created the device */
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dev_t backing_devno; /* The backing file's dev_t */
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ino_t backing_inode; /* The backing file's ino_t */
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uint64_t diskseq; /* Block device sequence number, monothonically incremented by the kernel on create/attach, or 0 if we don't know */
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uint32_t sector_size;
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uint64_t device_size;
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} LoopDevice;
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/* Returns true if LoopDevice object is not actually a loopback device but some other block device we just wrap */
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#define LOOP_DEVICE_IS_FOREIGN(d) ((d)->nr < 0)
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/* systemd-internal flags OR'd into the loop_flags argument of loop_device_make() and friends, in addition to
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* the kernel's LO_FLAGS_*. These live in high bits to stay clear of the kernel values and are masked out
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* before the flags reach the kernel.
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*
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* LOOP_DEVICE_MAY_POPULATE_PARTITION_TABLE: by default, when LO_FLAGS_PARTSCAN is requested but cannot be
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* enabled on the device and the device carries no partition table, we hand back the original fd instead of
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* allocating a loopback device — there's nothing to scan, and routing e.g. a multi-device btrfs member
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* through a loopback breaks it (https://github.com/systemd/systemd/issues/42520). Callers that might write a
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* (nested) partition table into the device and rely on partition scanning to pick it up afterwards must set
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* this flag to force a real loopback device even when the device is currently unpartitioned. */
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#define LOOP_DEVICE_MAY_POPULATE_PARTITION_TABLE (UINT32_C(1) << 16)
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int loop_device_make(int fd, int open_flags, uint64_t offset, uint64_t size, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret);
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int loop_device_make_by_path_at(int dir_fd, const char *path, int open_flags, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret);
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static inline int loop_device_make_by_path(const char *path, int open_flags, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret) {
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return loop_device_make_by_path_at(AT_FDCWD, path, open_flags, sector_size, loop_flags, lock_op, ret);
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}
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int loop_device_make_by_path_memory(const char *path, int open_flags, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret);
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int loop_device_open(sd_device *dev, int open_flags, int lock_op, LoopDevice **ret);
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int loop_device_open_from_fd(int fd, int open_flags, int lock_op, LoopDevice **ret);
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int loop_device_open_from_path(const char *path, int open_flags, int lock_op, LoopDevice **ret);
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DECLARE_TRIVIAL_REF_UNREF_FUNC(LoopDevice, loop_device);
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DEFINE_TRIVIAL_CLEANUP_FUNC(LoopDevice*, loop_device_unref);
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void loop_device_relinquish(LoopDevice *d);
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void loop_device_unrelinquish(LoopDevice *d);
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int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size);
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int loop_device_flock(LoopDevice *d, int operation);
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int loop_device_sync(LoopDevice *d);
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int loop_device_set_autoclear(LoopDevice *d, bool autoclear);
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int loop_device_set_filename(LoopDevice *d, const char *name);
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