On Freitag, 28. Juni 2019 12:09:31 CEST Greg Kurz wrote: > On Wed, 26 Jun 2019 20:42:13 +0200 > > Christian Schoenebeck via Qemu-devel <qemu-devel@nongnu.org> wrote: > > To support multiple devices on the 9p share, and avoid > > qid path collisions we take the device id as input > > to generate a unique QID path. The lowest 48 bits of > > the path will be set equal to the file inode, and the > > top bits will be uniquely assigned based on the top > > 16 bits of the inode and the device id. > > > > Signed-off-by: Antonios Motakis <antonios.mota...@huawei.com> > > Same remark about changes to the original patch.
ack_once(); :) > BTW, I had a concern with the way v9fs_do_readdir() open-codes QID > generation without calling stat_to_qid(). > > See discussion here: > > https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg02724.html > > I guess you should ensure in a preliminary patch that QIDs only > come out of stat_to_qid(). Mja, actually I first omitted your suggestion consciously, because I first thought it was an overkill pure visibility issue lmited to the default case remap_inodes==false, but now that I look at it again, it is actually an issue even when remap_inodes==true since dirent would expose wrong inode numbers on guest as well. I will see what to do about it. However about your other concern here, quote: "Also, if we hit a collision while reading the directory, I'm afraid the remaining entries won't be read at all. I'm not sure this is really what we want." That's however still a concern here that I would consider overkill to address. I mean if a user gets into that situation then because of a configuration error that must be corrected by user; the point of this patch set is to prevent undefined behaviour and to make the user aware about the root cause of the overall issue; the purpose is not to address all possible issues while there is still a configuration error. > > +static int qid_path_prefixmap(V9fsPDU *pdu, const struct stat *stbuf, > > + uint64_t *path) > > +{ > > + QppEntry lookup = { > > + .dev = stbuf->st_dev, > > + .ino_prefix = (uint16_t) (stbuf->st_ino >> 48) > > + }, *val; > > + uint32_t hash = qpp_hash(lookup); > > + > > + val = qht_lookup(&pdu->s->qpp_table, &lookup, hash); > > + > > + if (!val) { > > + if (pdu->s->qp_prefix_next == 0) { > > + /* we ran out of prefixes */ > > And we won't ever be able to allocate a new one. Maybe worth > adding an error_report_once() to inform the user ? Yeah, I thought about that as well. Will do. > > static int stat_to_qid(V9fsPDU *pdu, const struct stat *stbuf, V9fsQID > > *qidp) { > > > > - size_t size; > > + int err; > > > > - if (pdu->s->dev_id == 0) { > > - pdu->s->dev_id = stbuf->st_dev; > > - } else if (pdu->s->dev_id != stbuf->st_dev) { > > - error_report_once( > > - "9p: Multiple devices detected in same VirtFS export. " > > - "You must use a separate export for each device." > > - ); > > - return -ENOSYS; > > + if (pdu->s->ctx.export_flags & V9FS_REMAP_INODES) { > > + /* map inode+device to qid path (fast path) */ > > + err = qid_path_prefixmap(pdu, stbuf, &qidp->path); > > + if (err) { > > + return err; > > + } > > + } else { > > + if (pdu->s->dev_id == 0) { > > + pdu->s->dev_id = stbuf->st_dev; > > + } else if (pdu->s->dev_id != stbuf->st_dev) { > > + error_report_once( > > + "9p: Multiple devices detected in same VirtFS export. " > > + "You must either use a separate export for each device " > > + "shared from host or enable virtfs option > > 'remap_inodes'." > > + ); > > + return -ENOSYS; > > + } > > + size_t size; > > From CODING_STYLE: > > 5. Declarations > > Mixed declarations (interleaving statements and declarations within > blocks) are generally not allowed; declarations should be at the beginning > of blocks. > > Please do so for "size" and add an extra blank line. Ok. > > +#define QPATH_INO_MASK (((unsigned long)1 << 48) - 1) > > This won't give the expected result on a 32-bit host. Since this > is a mask for 64-bit entities, it should rather be: > > #define QPATH_INO_MASK ((1ULL << 48) - 1) Correct, will fix it. > > diff --git a/qemu-options.hx b/qemu-options.hx > > index 0d8beb4afd..e7ea136da1 100644 > > --- a/qemu-options.hx > > +++ b/qemu-options.hx > > @@ -1334,7 +1334,7 @@ ETEXI > > > > DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs, > > > > "-virtfs > > local,path=path,mount_tag=tag,security_model=mapped-xattr|mapped-fil > > e|passthrough|none\n"> > > - " > > [,id=id][,writeout=immediate][,readonly][,fmode=fmode][,dmode=dmode]\n" + > > " > > [,id=id][,writeout=immediate][,readonly][,fmode=fmode][,dmode=dmode][,rem > > ap_inodes]\n" > This feature applies to all backends IIUC. We don't really care for the > synth backend since it generates non-colliding inode numbers by design, > but the proxy backend has the same issue as local. So... Yeah, I was not sure about these, because I did not even know what these two were for exactly. :) [ lazyness disclaimer end] Will do for the other manual locations you mentioned as well. Best regards, Christian Schoenebeck
