[vfs] Allow mountpoint to be an existing non-directory.
Unlike linux mount(2), OCI spec allows mounting on top of an existing non-directory file. PiperOrigin-RevId: 327914342
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@ -18,12 +18,14 @@ import (
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"bytes"
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"fmt"
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"math"
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"path"
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"sort"
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"strings"
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"sync/atomic"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/context"
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"gvisor.dev/gvisor/pkg/fspath"
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"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
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"gvisor.dev/gvisor/pkg/syserror"
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)
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@ -888,6 +890,30 @@ func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRoo
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}
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}
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// MakeSyntheticMountpoint creates parent directories of target if they do not
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// exist and attempts to create a directory for the mountpoint. If a
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// non-directory file already exists there then we allow it.
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func (vfs *VirtualFilesystem) MakeSyntheticMountpoint(ctx context.Context, target string, root VirtualDentry, creds *auth.Credentials) error {
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mkdirOpts := &MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}
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// Make sure the parent directory of target exists.
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if err := vfs.MkdirAllAt(ctx, path.Dir(target), root, creds, mkdirOpts); err != nil {
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return fmt.Errorf("failed to create parent directory of mountpoint %q: %w", target, err)
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}
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// Attempt to mkdir the final component. If a file (of any type) exists
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// then we let allow mounting on top of that because we do not require the
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// target to be an existing directory, unlike Linux mount(2).
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if err := vfs.MkdirAt(ctx, creds, &PathOperation{
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Root: root,
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Start: root,
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Path: fspath.Parse(target),
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}, mkdirOpts); err != nil && err != syserror.EEXIST {
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return fmt.Errorf("failed to create mountpoint %q: %w", target, err)
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}
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return nil
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}
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// manglePath replaces ' ', '\t', '\n', and '\\' with their octal equivalents.
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// See Linux fs/seq_file.c:mangle_path.
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func manglePath(p string) string {
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@ -292,7 +292,7 @@ func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.C
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return nil, nil
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}
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if err := c.k.VFS().MkdirAllAt(ctx, submount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
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if err := c.k.VFS().MakeSyntheticMountpoint(ctx, submount.Destination, root, creds); err != nil {
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return nil, err
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}
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mnt, err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts)
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@ -496,7 +496,7 @@ func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *co
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root := mns.Root()
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defer root.DecRef(ctx)
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if err := c.k.VFS().MkdirAllAt(ctx, mount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
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if err := c.k.VFS().MakeSyntheticMountpoint(ctx, mount.Destination, root, creds); err != nil {
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return nil, err
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}
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