linux-ext4 - Re: [PATCH v3 04/13] ltp/fsx.c: Add atomic writes support to fsx

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Message-ID: <aH9g5jkwnXAkQUJl@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Tue, 22 Jul 2025 15:29:02 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Zorro Lang <zlang@...hat.com>, fstests@...r.kernel.org,
        Ritesh Harjani <ritesh.list@...il.com>, john.g.garry@...cle.com,
        tytso@....edu, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 04/13] ltp/fsx.c: Add atomic writes support to fsx

On Thu, Jul 17, 2025 at 09:17:47AM -0700, Darrick J. Wong wrote:

<snip>

> > +
> > +/*
> > + * Round down n to nearest power of 2.
> > + * If n is already a power of 2, return n;
> > + */
> > +static int rounddown_pow_of_2(int n) {
> > +	int i = 0;
> > +
> > +	if (is_power_of_2(n))
> > +		return n;
> > +
> > +	for (; (1 << i) < n; i++);
> > +
> > +	return 1 << (i - 1);
> > +}
> > +
> >  void
> >  dowrite(unsigned offset, unsigned size, int flags)
> >  {
> > @@ -1081,6 +1113,27 @@ dowrite(unsigned offset, unsigned size, int flags)
> >  	offset -= offset % writebdy;
> >  	if (o_direct)
> >  		size -= size % writebdy;
> > +	if (flags & RWF_ATOMIC) {
> > +		/* atomic write len must be inbetween awu_min and awu_max */
> > +		if (size < awu_min)
> > +			size = awu_min;
> > +		if (size > awu_max)
> > +			size = awu_max;
> > +
> > +		/* atomic writes need power-of-2 sizes */
> > +		size = rounddown_pow_of_2(size);
> > +
> > +		/* atomic writes need naturally aligned offsets */
> > +		offset -= offset % size;
> 
> I don't think you should be modifying offset/size here.  Normally for
> fsx we do all the rounding of the file range in the switch statement
> after the "calculate appropriate op to run" comment statement.
> 
> --D

Yes, I noticed that but then I saw we make size/offset adjustments in
do write for writebdy and I wanted atomic writes adjustments to be done
after that.

Regads,
ojaswin

> 
> > +
> > +		/* Skip the write if we are crossing max filesize */
> > +		if ((offset + size) > maxfilelen) {
> > +			if (!quiet && testcalls > simulatedopcount)
> > +				prt("skipping atomic write past maxfilelen\n");
> > +			log4(OP_WRITE_ATOMIC, offset, size, FL_SKIPPED);
> > +			return;
> > +		}
> > +	}
> >  	if (size == 0) {
> >  		if (!quiet && testcalls > simulatedopcount && !o_direct)
> >  			prt("skipping zero size write\n");
> > @@ -1088,7 +1141,10 @@ dowrite(unsigned offset, unsigned size, int flags)
> >  		return;
> >  	}
> >  
> > -	log4(OP_WRITE, offset, size, FL_NONE);
> > +	if (flags & RWF_ATOMIC)
> > +		log4(OP_WRITE_ATOMIC, offset, size, FL_NONE);
> > +	else
> > +		log4(OP_WRITE, offset, size, FL_NONE);
> >  
> >  	gendata(original_buf, good_buf, offset, size);
> >  	if (offset + size > file_size) {
> > @@ -1108,8 +1164,9 @@ dowrite(unsigned offset, unsigned size, int flags)
> >  		       (monitorstart == -1 ||
> >  			(offset + size > monitorstart &&
> >  			(monitorend == -1 || offset <= monitorend))))))
> > -		prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d\n", testcalls,
> > -		    offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0);
> > +		prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d atomic_wr=%d\n", testcalls,
> > +		    offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0,
> > +		    (flags & RWF_ATOMIC) != 0);
> >  	iret = fsxwrite(fd, good_buf + offset, size, offset, flags);
> >  	if (iret != size) {
> >  		if (iret == -1)
> > @@ -1785,6 +1842,30 @@ do_dedupe_range(unsigned offset, unsigned length, unsigned dest)
> >  }
> >  #endif
> >  
> > +int test_atomic_writes(void) {
> > +	int ret;
> > +	struct statx stx;
> > +