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vfs: provide F_ISUNIONSTACK as a kludge for libc
Prior to introduction of this op libc's readdir would call fstatfs(2), in effect unnecessarily copying kilobytes of data just to check fs name and a mount flag. Reviewed by: kib (previous version) Differential Revision: https://reviews.freebsd.org/D23162
This commit is contained in:
parent
360af171b3
commit
d3cc535474
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=356830
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@ -273,6 +273,24 @@ _filldir(DIR *dirp, bool use_current_pos)
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return (true);
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}
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static bool
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is_unionstack(int fd)
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{
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struct statfs sfb;
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int unionstack;
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unionstack = _fcntl(fd, F_ISUNIONSTACK);
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if (unionstack != -1)
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return (unionstack);
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/*
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* Temporary compat for kernels which don't provide F_ISUNIONSTACK.
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*/
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if (_fstatfs(fd, &sfb) < 0)
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return (true);
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return (strcmp(sfb.f_fstypename, "unionfs") == 0 ||
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(sfb.f_flags & MNT_UNION));
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}
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/*
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* Common routine for opendir(3), __opendir2(3) and fdopendir(3).
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@ -312,12 +330,7 @@ __opendir_common(int fd, int flags, bool use_current_pos)
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*/
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unionstack = false;
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if (flags & DTF_NODUP) {
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struct statfs sfb;
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if (_fstatfs(fd, &sfb) == 0) {
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unionstack = strcmp(sfb.f_fstypename, "unionfs") == 0 ||
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(sfb.f_flags & MNT_UNION);
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}
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unionstack = is_unionstack(fd);
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}
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if (unionstack) {
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@ -28,7 +28,7 @@
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.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
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.\" $FreeBSD$
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.\"
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.Dd September 4, 2019
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.Dd January 17, 2020
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.Dt FCNTL 2
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.Os
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.Sh NAME
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@ -185,6 +185,11 @@ Add seals to the file as described below, if the underlying filesystem supports
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seals.
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.It Dv F_GET_SEALS
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Get seals associated with the file, if the underlying filesystem supports seals.
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.It Dv F_ISUNIONSTACK
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Check if the vnode is part of a union stack (either the "union" flag from
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.Xr mount 2
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or unionfs).
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This is a hack not intended to be used outside of libc.
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.El
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.Pp
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The flags for the
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@ -296,7 +296,7 @@ unionfs_domount(struct mount *mp)
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if ((ump->um_lowervp->v_mount->mnt_flag & MNT_LOCAL) &&
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(ump->um_uppervp->v_mount->mnt_flag & MNT_LOCAL))
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mp->mnt_flag |= MNT_LOCAL;
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mp->mnt_kern_flag |= MNTK_NOMSYNC;
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mp->mnt_kern_flag |= MNTK_NOMSYNC | MNTK_UNIONFS;
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MNT_IUNLOCK(mp);
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/*
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@ -489,6 +489,7 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
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struct filedescent *fde;
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struct proc *p;
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struct vnode *vp;
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struct mount *mp;
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int error, flg, seals, tmp;
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uint64_t bsize;
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off_t foffset;
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@ -816,6 +817,49 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
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fdrop(fp, td);
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break;
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case F_ISUNIONSTACK:
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/*
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* Check if the vnode is part of a union stack (either the
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* "union" flag from mount(2) or unionfs).
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*
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* Prior to introduction of this op libc's readdir would call
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* fstatfs(2), in effect unnecessarily copying kilobytes of
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* data just to check fs name and a mount flag.
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*
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* Fixing the code to handle everything in the kernel instead
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* is a non-trivial endeavor and has low priority, thus this
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* horrible kludge facilitates the current behavior in a much
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* cheaper manner until someone(tm) sorts this out.
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*/
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error = fget_unlocked(fdp, fd, &cap_no_rights, &fp, NULL);
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if (error != 0)
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break;
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if (fp->f_type != DTYPE_VNODE) {
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fdrop(fp, td);
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error = EBADF;
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break;
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}
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vp = fp->f_vnode;
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/*
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* Since we don't prevent dooming the vnode even non-null mp
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* found can become immediately stale. This is tolerable since
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* mount points are type-stable (providing safe memory access)
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* and any vfs op on this vnode going forward will return an
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* error (meaning return value in this case is meaningless).
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*/
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mp = (struct mount *)atomic_load_ptr(&vp->v_mount);
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if (__predict_false(mp == NULL)) {
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fdrop(fp, td);
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error = EBADF;
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break;
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}
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td->td_retval[0] = 0;
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if (mp->mnt_kern_flag & MNTK_UNIONFS ||
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mp->mnt_flag & MNT_UNION)
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td->td_retval[0] = 1;
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fdrop(fp, td);
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break;
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default:
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error = EINVAL;
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break;
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@ -250,6 +250,7 @@ typedef __pid_t pid_t;
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#define F_DUP2FD_CLOEXEC 18 /* Like F_DUP2FD, but FD_CLOEXEC is set */
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#define F_ADD_SEALS 19
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#define F_GET_SEALS 20
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#define F_ISUNIONSTACK 21 /* Kludge for libc, don't use it. */
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/* Seals (F_ADD_SEALS, F_GET_SEALS). */
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#define F_SEAL_SEAL 0x0001 /* Prevent adding sealings */
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@ -414,6 +414,7 @@ void __mnt_vnode_markerfree_lazy(struct vnode **mvp, struct mount *mp);
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#define MNTK_USES_BCACHE 0x00004000 /* FS uses the buffer cache. */
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#define MNTK_TEXT_REFS 0x00008000 /* Keep use ref for text */
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#define MNTK_VMSETSIZE_BUG 0x00010000
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#define MNTK_UNIONFS 0x00020000 /* A hack for F_ISUNIONSTACK */
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#define MNTK_NOASYNC 0x00800000 /* disable async */
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#define MNTK_UNMOUNT 0x01000000 /* unmount in progress */
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#define MNTK_MWAIT 0x02000000 /* waiting for unmount to finish */
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