Yes, but it was enabled also before this patch series. Now I have checked that even old Linux 4.19 cifs kernel client detects empty file with system attribute as fifo. This functionality is there for a long time. Probably since first cifs/sfu version. On Friday 13 September 2024 17:33:22 Steve French wrote: > One other thing which worried me a bit is that I confirmed that an > empty file with the system attribute set was matched as a FIFO file > type (when you mount with "sfu") - this seems risky. > > On Fri, Sep 13, 2024 at 5:14 PM Steve French <smfrench@xxxxxxxxx> wrote: > > > > How did you find the format of the FIFO and SOCK file types? I > > couldn't find any references to those so added two new types to allow > > current Linux to be able to create these (especially since they are > > opaque to the server and thus low risk). > > > > > + case S_IFSOCK: > > > - strscpy(pdev.type, "LnxSOCK"); > > > + /* SFU socket is system file with one zero byte */ > > > + pdev_len = 1; > > > + pdev.type[0] = '\0'; > > > break; > > > case S_IFIFO: > > > - strscpy(pdev.type, "LnxFIFO"); > > > + /* SFU fifo is system file which is empty */ > > > + pdev_len = 0; > > > > My worry about the suggested change above is that it is possible that > > we could accidentally match to an empty file. We intentionally added > > the two new dev.type fields for these to avoid collisions with other > > things (and since they are Linux specific). It seems risky to have an > > empty file with the system attribute marked as a FIFO, and similarly a > > file with one byte null as Socket. Since this is for only the Linux > > client to recognize, I wanted to do something safe for those file > > types less likely to be confusing (ie strings for Socket and FIFO that > > were similar in length and format to the other special files seemed > > intuitive) and "LnxFIFO" and LnxSOCK" were used as the tags in the > > file to reduce confusion ie the tags for those two start with "Lnx" - > > ie "something used for Linux client" not related to the original > > Interix (those begin with "Intx"). > > > > Note that in the long run we hope to use reparse points by default in > > more servers to store special files like this but there are a few > > cases for unusual workloads that need special file support that would > > have to use sfu still. The newer reparse tags that Windows uses "WSL" > > have the advantage that they require fewer roundtrips to query (since > > the file type is in the reparse tag). > > > > Also noticed an interesting problem when mounted with "sfu" - > > "smbgetinfo filebasicinfo /mnt/fifo1" will hang (in sys_open). Is > > that expected for a FIFO? > > > > On Fri, Sep 13, 2024 at 3:07 PM Pali Rohár <pali@xxxxxxxxxx> wrote: > > > > > > On Thursday 12 September 2024 14:05:47 Pali Rohár wrote: > > > > SFU-style fifo is empty file with system attribute set. This format is used > > > > by old Microsoft POSIX subsystem and later also by OpenNT/Interix subsystem > > > > (which replaced Microsoft POSIX subsystem and is part of Microsoft SFU). > > > > > > > > SFU-style socket is file which has system attribute set and file content is > > > > one zero byte. This format was introduced in Interix 3.0 subsystem, as part > > > > of the Microsoft SFU 3.0 and is used also by all later versions. Previous > > > > versions had no UNIX domain socket support. > > > > > > > > Currently when sfu mount option is specified then CIFS creates fifo and > > > > socket special files with some strange LnxSOCK or LnxFIFO content which is > > > > not compatible with Microsoft SFU and neither recognized by other SMB > > > > implementations which have some SFU support, including older Linux cifs > > > > implementations. > > > > > > > > So when sfu mount option is specified, create all fifo and socket special > > > > files compatible with SFU format to achieve SFU interop, as it is expected > > > > by sfu mount option. > > > > > > > > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx> > > > > > > Fixes: 72bc63f5e23a ("smb3: fix creating FIFOs when mounting with "sfu" mount option") > > > Fixes: 518549c120e6 ("cifs: fix creating sockets when using sfu mount options") > > > > > > I located commits which introduced those strange LnxSOCK or LnxFIFO > > > types which are not compatible with SFU. I would suggest to add those > > > two Fixes: tags into commit message for reference. > > > > > > > --- > > > > fs/smb/client/cifssmb.c | 8 ++++---- > > > > fs/smb/client/smb1ops.c | 2 +- > > > > fs/smb/client/smb2ops.c | 29 +++++++++++++++++++---------- > > > > 3 files changed, 24 insertions(+), 15 deletions(-) > > > > > > > > diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c > > > > index cfae2e918209..0ffc45aa5e2c 100644 > > > > --- a/fs/smb/client/cifssmb.c > > > > +++ b/fs/smb/client/cifssmb.c > > > > @@ -1076,8 +1076,8 @@ SMBLegacyOpen(const unsigned int xid, struct cifs_tcon *tcon, > > > > pSMB->OpenFlags |= cpu_to_le16(REQ_MORE_INFO); > > > > pSMB->Mode = cpu_to_le16(access_flags_to_smbopen_mode(access_flags)); > > > > pSMB->Mode |= cpu_to_le16(0x40); /* deny none */ > > > > - /* set file as system file if special file such > > > > - as fifo and server expecting SFU style and > > > > + /* set file as system file if special file such as fifo, > > > > + * socket, char or block and server expecting SFU style and > > > > no Unix extensions */ > > > > > > > > if (create_options & CREATE_OPTION_SPECIAL) > > > > @@ -1193,8 +1193,8 @@ CIFS_open(const unsigned int xid, struct cifs_open_parms *oparms, int *oplock, > > > > req->AllocationSize = 0; > > > > > > > > /* > > > > - * Set file as system file if special file such as fifo and server > > > > - * expecting SFU style and no Unix extensions. > > > > + * Set file as system file if special file such as fifo, socket, char > > > > + * or block and server expecting SFU style and no Unix extensions. > > > > */ > > > > if (create_options & CREATE_OPTION_SPECIAL) > > > > req->FileAttributes = cpu_to_le32(ATTR_SYSTEM); > > > > diff --git a/fs/smb/client/smb1ops.c b/fs/smb/client/smb1ops.c > > > > index e1f2feb56f45..e03c91a49650 100644 > > > > --- a/fs/smb/client/smb1ops.c > > > > +++ b/fs/smb/client/smb1ops.c > > > > @@ -1078,7 +1078,7 @@ cifs_make_node(unsigned int xid, struct inode *inode, > > > > /* > > > > * Check if mounted with mount parm 'sfu' mount parm. > > > > * SFU emulation should work with all servers, but only > > > > - * supports block and char device (no socket & fifo), > > > > + * supports block and char device, socket & fifo, > > > > * and was used by default in earlier versions of Windows > > > > */ > > > > if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL)) > > > > diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c > > > > index 9c2d065d3cc4..9e90672caf60 100644 > > > > --- a/fs/smb/client/smb2ops.c > > > > +++ b/fs/smb/client/smb2ops.c > > > > @@ -5066,26 +5066,32 @@ static int __cifs_sfu_make_node(unsigned int xid, struct inode *inode, > > > > struct cifs_fid fid; > > > > unsigned int bytes_written; > > > > struct win_dev pdev = {}; > > > > + size_t pdev_len = 0; > > > > struct kvec iov[2]; > > > > __u32 oplock = server->oplocks ? REQ_OPLOCK : 0; > > > > int rc; > > > > > > > > switch (mode & S_IFMT) { > > > > case S_IFCHR: > > > > + pdev_len = sizeof(pdev); > > > > memcpy(pdev.type, "IntxCHR\0", 8); > > > > pdev.major = cpu_to_le64(MAJOR(dev)); > > > > pdev.minor = cpu_to_le64(MINOR(dev)); > > > > break; > > > > case S_IFBLK: > > > > + pdev_len = sizeof(pdev); > > > > memcpy(pdev.type, "IntxBLK\0", 8); > > > > pdev.major = cpu_to_le64(MAJOR(dev)); > > > > pdev.minor = cpu_to_le64(MINOR(dev)); > > > > break; > > > > case S_IFSOCK: > > > > - strscpy(pdev.type, "LnxSOCK"); > > > > + /* SFU socket is system file with one zero byte */ > > > > + pdev_len = 1; > > > > + pdev.type[0] = '\0'; > > > > break; > > > > case S_IFIFO: > > > > - strscpy(pdev.type, "LnxFIFO"); > > > > + /* SFU fifo is system file which is empty */ > > > > + pdev_len = 0; > > > > break; > > > > default: > > > > return -EPERM; > > > > @@ -5100,14 +5106,17 @@ static int __cifs_sfu_make_node(unsigned int xid, struct inode *inode, > > > > if (rc) > > > > return rc; > > > > > > > > - io_parms.pid = current->tgid; > > > > - io_parms.tcon = tcon; > > > > - io_parms.length = sizeof(pdev); > > > > - iov[1].iov_base = &pdev; > > > > - iov[1].iov_len = sizeof(pdev); > > > > + if (pdev_len > 0) { > > > > + io_parms.pid = current->tgid; > > > > + io_parms.tcon = tcon; > > > > + io_parms.length = pdev_len; > > > > + iov[1].iov_base = &pdev; > > > > + iov[1].iov_len = pdev_len; > > > > + > > > > + rc = server->ops->sync_write(xid, &fid, &io_parms, > > > > + &bytes_written, iov, 1); > > > > + } > > > > > > > > - rc = server->ops->sync_write(xid, &fid, &io_parms, > > > > - &bytes_written, iov, 1); > > > > server->ops->close(xid, tcon, &fid); > > > > return rc; > > > > } > > > > @@ -5149,7 +5158,7 @@ static int smb2_make_node(unsigned int xid, struct inode *inode, > > > > /* > > > > * Check if mounted with mount parm 'sfu' mount parm. > > > > * SFU emulation should work with all servers, but only > > > > - * supports block and char device (no socket & fifo), > > > > + * supports block and char device, socket & fifo, > > > > * and was used by default in earlier versions of Windows > > > > */ > > > > if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL) { > > > > -- > > > > 2.20.1 > > > > > > > > > > > > > -- > > Thanks, > > > > Steve > > > > -- > Thanks, > > Steve