Fix inconsistent mount options for ZFS root #16646
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While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Signed-off-by: Umer Saleem <[email protected]>
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While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Ameer Hamza <[email protected]> Signed-off-by: Umer Saleem <[email protected]> Closes openzfs#16646
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While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Ameer Hamza <[email protected]> Signed-off-by: Umer Saleem <[email protected]> Closes openzfs#16646
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While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Ameer Hamza <[email protected]> Signed-off-by: Umer Saleem <[email protected]> Closes openzfs#16646
This was referenced Oct 21, 2024
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While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Ameer Hamza <[email protected]> Signed-off-by: Umer Saleem <[email protected]> Closes openzfs#16646
behlendorf
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Oct 21, 2024
While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes mount system call directly. This skips the ZFS helper mount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties. There has been an attempt to use mount.zfs in zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and other child datasets of root have the same issue (Issue#9461). This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds 'mntpoint=/root' to the mount options, which is then prepended to the snapshot mountpoint in '.zfs/snapshot'. '/root' is the directory on Debian with initramfs-tools where root filesystem is mounted before pivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on '/root/.zfs/*', which fails. This commit attempts to fix the automounting of snapshots on root, while using mount.zfs in initrd script. Since the mountpoint of dataset is stored in vfs_mntpoint field, we can check if current mountpoint of dataset and vfs_mntpoint are same or not. If they are not same, reset the vfs_mntpoint field with current mountpoint. This fixes the mountpoints of root dataset and children in respective vfs_mntpoint fields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored in vfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible. This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (d_path), returns the complete path for given struct path. It works in chroot environment as well and returns the correct path from original filesystem root. However d_path fails to return the complete path if any directory from original root filesystem is mounted using --bind flag or --rbind flag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment, d_path returns the path correctly, i.e. it returns the correct path to the directory that is mounted with --bind flag. However inside the chroot environment, it only returns the path inside chroot. For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with --bind or --rbind on another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context. With the snapshots issue fixed for root filesystem, using mount.zfs in ZFS initrd script, mounts the datasets with correct mount options. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Ameer Hamza <[email protected]> Signed-off-by: Umer Saleem <[email protected]> Closes openzfs#16646
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Motivation and Context
On Linux, ZFS root is mounted with inconsistent mount options. Moreover, automounting of snapshots breaks on root if
mount.zfsis used to mount the ZFS root during boot. This PR attempts to fix both these issues.Description
While mounting ZFS root during boot on Linux distributions from initrd, mount from busybox is effectively used which executes
mountsystem call directly. This skips the ZFS helpermount.zfs, which checks and enables the mount options as specified in dataset properties. As a result, datasets mounted during boot from initrd do not have correct mount options as specified in ZFS dataset properties.There has been an attempt to use
mount.zfsin zfs initrd script, responsible for mounting the ZFS root filesystem (PR#13305). This was later reverted (PR#14908) after discovering that using mount.zfs breaks mounting of snapshots on root (/) and child datasets of root have the same issue (Issue#9461).This happens because switching from busybox mount to mount.zfs correctly parses the mount options but also adds
mntpoint=/rootto the mount options, which is then prepended to the snapshot mountpoint in.zfs/snapshot./rootis the directory on Debian withinitramfs-toolswhere root filesystem is mounted beforepivot_root. When Linux runtime is reached, trying to access the snapshots on root results in automounting the snapshot on/root/.zfs/*, which fails.This commit attempts to fix the automounting of snapshots on root, while using
mount.zfsin initrd script. Since the mountpoint of dataset is stored invfs_mntpointfield, we can check if current mountpoint of dataset andvfs_mntpointare same or not. If they are not same, reset thevfs_mntpointfield with current mountpoint. This fixes the mountpoints of root dataset and children in respectivevfs_mntpointfields when we try to access the snapshots of root dataset or its children. With correct mountpoint for root dataset and children stored invfs_mntpoint, all snapshots of root dataset are mounted correctly and become accessible.This fix will come into play only if current process, that is trying to access the snapshots is not in chroot context. The Linux kernel API that is used to convert struct path into char format (
d_path), returns the complete path for givenstruct path. It works in chroot environment as well and returns the correct path from original filesystem root.However,
d_pathfails to return the complete path if any directory from original root filesystem is mounted using--bindflag or--rbindflag in chroot environment. In this case, if we try to access the snapshot from outside the chroot environment,d_pathreturns the path correctly, i.e. it returns the correct path to the directory that is mounted with--bindflag. However inside the chroot environment, it only returns the path inside chroot.For now, there is not a better way in my understanding that gives the complete path in char format and handles the case where directories from root filesystem are mounted with
--bindor--rbindon another path which user will later chroot into. So this fix gets enabled if current process trying to access the snapshot is not in chroot context.With the snapshots issue fixed for root filesystem, using
mount.zfsin ZFS initrd script, mounts the datasets with correct mount options.How Has This Been Tested?
/while usingmount.zfsto mount ZFS root during boot.--bind/--rbindcase)Types of changes
Checklist:
Signed-off-by.