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vfs: Fix "emptydir" mount option

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Fix vfs_emptydir(). It would consider directories containing directories
with name of the form 'X.' (X being any authorized byte) as empty. Also,
it would cause VOP_READDIR() to return an error on directories
containing enough whiteouts. While here, use a more decently sized
buffer as done elsewhere.

Remove ad-hoc iteration on the directory's content and instead use the
newly exported vn_dir_next_dirent() function (this is what fixes the
second problem mentioned above).

PR:	270988
Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D39775
This commit is contained in:
Olivier Certner 2023-04-22 18:07:07 +02:00 committed by Konstantin Belousov
parent 3d8450db4c
commit 6450e7bbad
1 changed files with 68 additions and 49 deletions
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117
sys/kern/vfs_subr.c
View file

@ -6391,65 +6391,84 @@ filt_vfsvnode(struct knote *kn, long hint)
int
vfs_emptydir(struct vnode *vp)
{
struct uio uio;
struct iovec iov;
struct dirent *dirent, *dp, *endp;
int error, eof;
error = 0;
eof = 0;
struct thread *const td = curthread;
char *dirbuf;
size_t dirbuflen, len;
off_t off;
int eofflag, error;
struct dirent *dp;
struct vattr va;
ASSERT_VOP_LOCKED(vp, "vfs_emptydir");
VNPASS(vp->v_type == VDIR, vp);
dirent = malloc(sizeof(struct dirent), M_TEMP, M_WAITOK);
iov.iov_base = dirent;
iov.iov_len = sizeof(struct dirent);
error = VOP_GETATTR(vp, &va, td->td_ucred);
if (error != 0)
return (error);
uio.uio_iov = &iov;
uio.uio_iovcnt = 1;
uio.uio_offset = 0;
uio.uio_resid = sizeof(struct dirent);
uio.uio_segflg = UIO_SYSSPACE;
uio.uio_rw = UIO_READ;
uio.uio_td = curthread;
dirbuflen = max(DEV_BSIZE, GENERIC_MAXDIRSIZ);
if (dirbuflen < va.va_blocksize)
dirbuflen = va.va_blocksize;
dirbuf = malloc(dirbuflen, M_TEMP, M_WAITOK);
while (eof == 0 && error == 0) {
error = VOP_READDIR(vp, &uio, curthread->td_ucred, &eof,
NULL, NULL);
len = 0;
off = 0;
eofflag = 0;
for (;;) {
error = vn_dir_next_dirent(vp, td, dirbuf, dirbuflen,
&dp, &len, &off, &eofflag);
if (error != 0)
goto end;
if (len == 0) {
/* EOF */
error = 0;
goto end;
}
/*
* Skip whiteouts. Unionfs operates on filesystems only and not
* on hierarchies, so these whiteouts would be shadowed on the
* system hierarchy but not for a union using the filesystem of
* their directories as the upper layer. Additionally, unionfs
* currently transparently exposes union-specific metadata of
* its upper layer, meaning that whiteouts can be seen through
* the union view in empty directories. Taking into account
* these whiteouts would then prevent mounting another
* filesystem on such effectively empty directories.
*/
if (dp->d_type == DT_WHT)
continue;
/*
* Any file in the directory which is not '.' or '..' indicates
* the directory is not empty.
*/
switch (dp->d_namlen) {
case 2:
if (dp->d_name[1] != '.') {
/* Can't be '..' (nor '.') */
error = ENOTEMPTY;
goto end;
}
/* FALLTHROUGH */
case 1:
if (dp->d_name[0] != '.') {
/* Can't be '..' nor '.' */
error = ENOTEMPTY;
goto end;
}
break;
endp = (void *)((uint8_t *)dirent +
sizeof(struct dirent) - uio.uio_resid);
for (dp = dirent; dp < endp;
dp = (void *)((uint8_t *)dp + GENERIC_DIRSIZ(dp))) {
if (dp->d_type == DT_WHT)
continue;
if (dp->d_namlen == 0)
continue;
if (dp->d_type != DT_DIR &&
dp->d_type != DT_UNKNOWN) {
error = ENOTEMPTY;
break;
}
if (dp->d_namlen > 2) {
error = ENOTEMPTY;
break;
}
if (dp->d_namlen == 1 &&
dp->d_name[0] != '.') {
error = ENOTEMPTY;
break;
}
if (dp->d_namlen == 2 &&
dp->d_name[1] != '.') {
error = ENOTEMPTY;
break;
}
uio.uio_resid = sizeof(struct dirent);
default:
error = ENOTEMPTY;
goto end;
}
}
free(dirent, M_TEMP);
end:
free(dirbuf, M_TEMP);
return (error);
}