Re: [PATCH] cifs: only write 64kb at a time when fallocating a small region of a file

[Steve French <smfrench@gmail.com>]

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Removed the deletion from the patch, and added Reported-by: Namjae ...
and pushed to cifs-2.6.git for-next

On Thu, Jul 22, 2021 at 2:19 AM ronnie sahlberg
<ronniesahlberg@gmail.com> wrote:
>
> Yes, ofcourse.
>
> Steve, can you revert that deletion in the patch?
>
> On Thu, Jul 22, 2021 at 4:55 PM Namjae Jeon <namjae.jeon@samsung.com> wrote:
> >
> > > This code is actually bogus and does the opposite of what the comment says.
> > > If out_data_len is 0 then that means that the entire region is unallocated and then we should not
> > > bail out but proceed and allocate the hole.
> >
> > > generic/071 works against a windows server for me.
> >
> >
> > > If it fails with this code removed it might mean that generic/071 never worked with cifs.ko correctly.
> >
> > generic/071 create preallocated extent by calling fallocate with keep size flags.
> > It means the file size should not be increased.
> > But if (out_buf_len == 0) check is removed, 1MB write is performed using SMB2_write loop().
> > It means the file size becomes 1MB.
> >
> > And then, generic/071 call again fallocate(0, 512K) which mean file size should be 512K.
> > but SMB2_set_eof() in cifs is not called due to the code below(->i_size is bigger than off + len),
> > So 071 test failed as file size remains 1MB.
> >
> >         /*
> >          * Extending the file
> >          */
> >         if ((keep_size == false) && i_size_read(inode) < off + len) {
> >                 rc = inode_newsize_ok(inode, off + len);
> >                 if (rc)
> >                         goto out;
> >
> >                 if ((cifsi->cifsAttrs & FILE_ATTRIBUTE_SPARSE_FILE) == 0)
> >                         smb2_set_sparse(xid, tcon, cfile, inode, false);
> >
> >                 eof = cpu_to_le64(off + len);
> >                 rc = SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
> >                                   cfile->fid.volatile_fid, cfile->pid, &eof);
> >                 if (rc == 0) {
> >                         cifsi->server_eof = off + len;
> >                         cifs_setsize(inode, off + len);
> >                         cifs_truncate_page(inode->i_mapping, inode->i_size);
> >                         truncate_setsize(inode, off + len);
> >                 }
> >                 goto out;
> >         }
> >



-- 
Thanks,

Steve

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From 2485bd7557a7edb4520b4072af464f0a08c8efe0 Mon Sep 17 00:00:00 2001
From: Ronnie Sahlberg <lsahlber@redhat.com>
Date: Thu, 22 Jul 2021 14:53:32 +1000
Subject: [PATCH 1/2] cifs: only write 64kb at a time when fallocating a small
 region of a file

We only allow sending single credit writes through the SMB2_write() synchronous
api so split this into smaller chunks.

Fixes: 966a3cb7c7db ("cifs: improve fallocate emulation")

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reported-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/smb2ops.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index ba3c58e1f725..5cefb5972396 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -3617,7 +3617,7 @@ static int smb3_simple_fallocate_write_range(unsigned int xid,
 					     char *buf)
 {
 	struct cifs_io_parms io_parms = {0};
-	int nbytes;
+	int rc, nbytes;
 	struct kvec iov[2];
 
 	io_parms.netfid = cfile->fid.netfid;
@@ -3625,13 +3625,25 @@ static int smb3_simple_fallocate_write_range(unsigned int xid,
 	io_parms.tcon = tcon;
 	io_parms.persistent_fid = cfile->fid.persistent_fid;
 	io_parms.volatile_fid = cfile->fid.volatile_fid;
-	io_parms.offset = off;
-	io_parms.length = len;
 
-	/* iov[0] is reserved for smb header */
-	iov[1].iov_base = buf;
-	iov[1].iov_len = io_parms.length;
-	return SMB2_write(xid, &io_parms, &nbytes, iov, 1);
+	while (len) {
+		io_parms.offset = off;
+		io_parms.length = len;
+		if (io_parms.length > SMB2_MAX_BUFFER_SIZE)
+			io_parms.length = SMB2_MAX_BUFFER_SIZE;
+		/* iov[0] is reserved for smb header */
+		iov[1].iov_base = buf;
+		iov[1].iov_len = io_parms.length;
+		rc = SMB2_write(xid, &io_parms, &nbytes, iov, 1);
+		if (rc)
+			break;
+		if (nbytes > len)
+			return -EINVAL;
+		buf += nbytes;
+		off += nbytes;
+		len -= nbytes;
+	}
+	return rc;
 }
 
 static int smb3_simple_fallocate_range(unsigned int xid,
-- 
2.30.2