NFS: Add static NFS I/O tracepoints

Tools like tcpdump and rpcdebug can be very useful. But there are
plenty of environments where they are difficult or impossible to
use. For example, we've had customers report I/O failures during
workloads so heavy that collecting network traffic or enabling
RPC debugging are themselves onerous.

The kernel's static tracepoints are lightweight (less likely to
introduce timing changes) and efficient (the trace data is compact).
They also work in scenarios where capturing network traffic is not
possible due to lack of hardware support (some InfiniBand HCAs) or
where data or network privacy is a concern.

Introduce tracepoints that show when an NFS READ, WRITE, or COMMIT
is initiated, and when it completes. Record the arguments and
results of each operation, which are not shown by existing sunrpc
module's tracepoints.

For instance, the recorded offset and count can be used to match an
"initiate" event to a "done" event. If an NFS READ result returns
fewer bytes than requested or zero, seeing the EOF flag can be
probative. Seeing an NFS4ERR_BAD_STATEID result is also indication
of a particular class of problems. The timing information attached
to each event record can often be useful as well.

Usage example:

[root@manet tmp]# trace-cmd record -e nfs:*initiate* -e nfs:*done
/sys/kernel/debug/tracing/events/nfs/*initiate*/filter
/sys/kernel/debug/tracing/events/nfs/*done/filter
Hit Ctrl^C to stop recording
^CKernel buffer statistics:
Note: "entries" are the entries left in the kernel ring buffer and are not
recorded in the trace data. They should all be zero.

CPU: 0
entries: 0
overrun: 0
commit overrun: 0
bytes: 3680
oldest event ts: 78.367422
now ts: 100.124419
dropped events: 0
read events: 74

... and so on.

Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>

fs/nfs/nfstrace.h

···
 			__get_str(name)
 		)
 );
+
+TRACE_EVENT(nfs_initiate_read,
+		TP_PROTO(
+			const struct inode *inode,
+			loff_t offset, unsigned long count
+		),
+
+		TP_ARGS(inode, offset, count),
+
+		TP_STRUCT__entry(
+			__field(loff_t, offset)
+			__field(unsigned long, count)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->offset = offset;
+			__entry->count = count;
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld count=%lu",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->count
+		)
+);
+
+TRACE_EVENT(nfs_readpage_done,
+		TP_PROTO(
+			const struct inode *inode,
+			int status, loff_t offset, bool eof
+		),
+
+		TP_ARGS(inode, status, offset, eof),
+
+		TP_STRUCT__entry(
+			__field(int, status)
+			__field(loff_t, offset)
+			__field(bool, eof)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->status = status;
+			__entry->offset = offset;
+			__entry->eof = eof;
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld status=%d%s",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->status,
+			__entry->eof ? " eof" : ""
+		)
+);
+
+/*
+ * XXX: I tried using NFS_UNSTABLE and friends in this table, but they
+ * all evaluate to 0 for some reason, even if I include linux/nfs.h.
+ */
+#define nfs_show_stable(stable) \
+	__print_symbolic(stable, \
+			{ 0, " (UNSTABLE)" }, \
+			{ 1, " (DATA_SYNC)" }, \
+			{ 2, " (FILE_SYNC)" })
+
+TRACE_EVENT(nfs_initiate_write,
+		TP_PROTO(
+			const struct inode *inode,
+			loff_t offset, unsigned long count,
+			enum nfs3_stable_how stable
+		),
+
+		TP_ARGS(inode, offset, count, stable),
+
+		TP_STRUCT__entry(
+			__field(loff_t, offset)
+			__field(unsigned long, count)
+			__field(enum nfs3_stable_how, stable)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->offset = offset;
+			__entry->count = count;
+			__entry->stable = stable;
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld count=%lu stable=%d%s",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->count,
+			__entry->stable, nfs_show_stable(__entry->stable)
+		)
+);
+
+TRACE_EVENT(nfs_writeback_done,
+		TP_PROTO(
+			const struct inode *inode,
+			int status,
+			loff_t offset,
+			struct nfs_writeverf *writeverf
+		),
+
+		TP_ARGS(inode, status, offset, writeverf),
+
+		TP_STRUCT__entry(
+			__field(int, status)
+			__field(loff_t, offset)
+			__field(enum nfs3_stable_how, stable)
+			__field(unsigned long long, verifier)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->status = status;
+			__entry->offset = offset;
+			__entry->stable = writeverf->committed;
+			memcpy(&__entry->verifier, &writeverf->verifier,
+			       sizeof(__entry->verifier));
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld status=%d stable=%d%s "
+			"verifier 0x%016llx",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->status,
+			__entry->stable, nfs_show_stable(__entry->stable),
+			__entry->verifier
+		)
+);
+
+TRACE_EVENT(nfs_initiate_commit,
+		TP_PROTO(
+			const struct nfs_commit_data *data
+		),
+
+		TP_ARGS(data),
+
+		TP_STRUCT__entry(
+			__field(loff_t, offset)
+			__field(unsigned long, count)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct inode *inode = data->inode;
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->offset = data->args.offset;
+			__entry->count = data->args.count;
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld count=%lu",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->count
+		)
+);
+
+TRACE_EVENT(nfs_commit_done,
+		TP_PROTO(
+			const struct nfs_commit_data *data
+		),
+
+		TP_ARGS(data),
+
+		TP_STRUCT__entry(
+			__field(int, status)
+			__field(loff_t, offset)
+			__field(unsigned long long, verifier)
+			__field(dev_t, dev)
+			__field(u32, fhandle)
+			__field(u64, fileid)
+		),
+
+		TP_fast_assign(
+			const struct inode *inode = data->inode;
+			const struct nfs_inode *nfsi = NFS_I(inode);
+
+			__entry->status = data->res.op_status;
+			__entry->offset = data->args.offset;
+			memcpy(&__entry->verifier, &data->verf.verifier,
+			       sizeof(__entry->verifier));
+			__entry->dev = inode->i_sb->s_dev;
+			__entry->fileid = nfsi->fileid;
+			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
+		),
+
+		TP_printk(
+			"fileid=%02x:%02x:%llu fhandle=0x%08x "
+			"offset=%lld status=%d verifier 0x%016llx",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			(unsigned long long)__entry->fileid,
+			__entry->fhandle,
+			__entry->offset, __entry->status,
+			__entry->verifier
+		)
+);
+
 #endif /* _TRACE_NFS_H */
 
 #undef TRACE_INCLUDE_PATH

fs/nfs/read.c

···
 #include "iostat.h"
 #include "fscache.h"
 #include "pnfs.h"
+#include "nfstrace.h"
 
 #define NFSDBG_FACILITY		NFSDBG_PAGECACHE
 
···
 
 	task_setup_data->flags |= swap_flags;
 	rpc_ops->read_setup(hdr, msg);
+	trace_nfs_initiate_read(inode, hdr->io_start, hdr->good_bytes);
 }
 
 static void
···
 		return status;
 
 	nfs_add_stats(inode, NFSIOS_SERVERREADBYTES, hdr->res.count);
+	trace_nfs_readpage_done(inode, task->tk_status,
+				hdr->args.offset, hdr->res.eof);
 
 	if (task->tk_status == -ESTALE) {
 		set_bit(NFS_INO_STALE, &NFS_I(inode)->flags);

fs/nfs/write.c

···
 
 	task_setup_data->priority = priority;
 	rpc_ops->write_setup(hdr, msg);
+	trace_nfs_initiate_write(hdr->inode, hdr->io_start, hdr->good_bytes,
+				 hdr->args.stable);
 
 	nfs4_state_protect_write(NFS_SERVER(hdr->inode)->nfs_client,
 				 &task_setup_data->rpc_client, msg, hdr);
···
 	status = NFS_PROTO(inode)->write_done(task, hdr);
 	if (status != 0)
 		return status;
+
 	nfs_add_stats(inode, NFSIOS_SERVERWRITTENBYTES, hdr->res.count);
+	trace_nfs_writeback_done(inode, task->tk_status,
+				 hdr->args.offset, hdr->res.verf);
 
 	if (hdr->res.verf->committed < hdr->args.stable &&
 	    task->tk_status >= 0) {
···
 	};
 	/* Set up the initial task struct.  */
 	nfs_ops->commit_setup(data, &msg);
+	trace_nfs_initiate_commit(data);
 
 	dprintk("NFS: initiated commit call\n");
 
···
 
 	/* Call the NFS version-specific code */
 	NFS_PROTO(data->inode)->commit_done(task, data);
+	trace_nfs_commit_done(data);
 }
 
 static void nfs_commit_release_pages(struct nfs_commit_data *data)