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From:   Thiago Becker <tbecker@redhat.com>
To:     linux-nfs@vger.kernel.org
Cc:     steved@redhat.com, trond.myklebust@hammerspace.com,
        anna.schumaker@netapp.com, kolga@netapp.com,
        Thiago Becker <tbecker@redhat.com>
Subject: [PATCH RFC v3 3/6] nfsrahead: only set readahead for nfs devices.
Date:   Wed, 23 Mar 2022 17:18:38 -0300
Message-Id: <20220323201841.4166549-4-tbecker@redhat.com>
In-Reply-To: <20220323201841.4166549-1-tbecker@redhat.com>
References: <20220323201841.4166549-1-tbecker@redhat.com>
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Limit setting the readahead for nfs devices.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1946283
Signed-off-by: Thiago Becker <tbecker@redhat.com>
---
 tools/nfsrahead/Makefile.am |   1 +
 tools/nfsrahead/main.c      | 130 ++++++++++++++++++++++++++++++++++++
 2 files changed, 131 insertions(+)

diff --git a/tools/nfsrahead/Makefile.am b/tools/nfsrahead/Makefile.am
index b598bec3..afccc520 100644
--- a/tools/nfsrahead/Makefile.am
+++ b/tools/nfsrahead/Makefile.am
@@ -1,5 +1,6 @@
 libexec_PROGRAMS = nfsrahead
 nfsrahead_SOURCES = main.c
+nfsrahead_LDFLAGS= -lmount
 
 udev_rulesdir = /etc/udev/rules.d
 udev_rules_DATA = 99-nfs_bdi.rules
diff --git a/tools/nfsrahead/main.c b/tools/nfsrahead/main.c
index e454108e..2cf77424 100644
--- a/tools/nfsrahead/main.c
+++ b/tools/nfsrahead/main.c
@@ -1,7 +1,137 @@
 #include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include <libmount/libmount.h>
+#include <sys/sysmacros.h>
+
+#ifndef MOUNTINFO_PATH
+#define MOUNTINFO_PATH "/proc/self/mountinfo"
+#endif
+
+/* Device information from the system */
+struct device_info {
+	char *device_number;
+	dev_t dev;
+	char *mountpoint;
+	char *fstype;
+};
+
+/* Convert a string in the format n:m to a device number */
+static dev_t dev_from_arg(const char *device_number)
+{
+	char *s = strdup(device_number), *p;
+	char *maj_s, *min_s;
+	unsigned int maj, min;
+	dev_t dev;
+
+	maj_s = p = s;
+	for ( ; *p != ':'; p++)
+		;
+
+	*p = '\0';
+	min_s = p + 1;
+
+	maj = strtol(maj_s, NULL, 10);
+	min = strtol(min_s, NULL, 10);
+
+	dev = makedev(maj, min);
+
+	free(s);
+	return dev;
+}
+
+#define sfree(ptr) if (ptr) free(ptr)
+
+/* device_info maintenance */
+static void init_device_info(struct device_info *di, const char *device_number)
+{
+	di->device_number = strdup(device_number);
+	di->dev = dev_from_arg(device_number);
+	di->mountpoint = NULL;
+	di->fstype = NULL;
+}
+
+
+static void free_device_info(struct device_info *di)
+{
+	sfree(di->mountpoint);
+	sfree(di->fstype);
+	sfree(di->device_number);
+}
+
+static int get_mountinfo(const char *device_number, struct device_info *device_info, const char *mountinfo_path)
+{
+	int ret = 0;
+	struct libmnt_table *mnttbl;
+	struct libmnt_fs *fs;
+	char *target;
+
+	init_device_info(device_info, device_number);
+
+	mnttbl = mnt_new_table();
+
+	if ((ret = mnt_table_parse_file(mnttbl, mountinfo_path)) < 0)
+		goto out_free_tbl;
+
+	if ((fs = mnt_table_find_devno(mnttbl, device_info->dev, MNT_ITER_FORWARD)) == NULL) {
+		ret = ENOENT;
+		goto out_free_tbl;
+	}
+
+	if ((target = (char *)mnt_fs_get_target(fs)) == NULL) {
+		ret = ENOENT;
+		goto out_free_fs;
+	}
+
+	device_info->mountpoint = strdup(target);
+	target = (char *)mnt_fs_get_fstype(fs);
+	if (target)
+		device_info->fstype = strdup(target);
+
+out_free_fs:
+	mnt_free_fs(fs);
+out_free_tbl:
+	mnt_free_table(mnttbl);
+	free(device_info->device_number);
+	device_info->device_number = NULL;
+	return ret;
+}
+
+static int get_device_info(const char *device_number, struct device_info *device_info)
+{
+	int ret = ENOENT;
+	for (int retry_count = 0; retry_count < 10 && ret != 0; retry_count++)
+		ret = get_mountinfo(device_number, device_info, MOUNTINFO_PATH);
+
+	return ret;
+}
 
 int main(int argc, char **argv, char **envp)
 {
+	int ret = 0;
+	struct device_info device;
 	unsigned int readahead = 128;
+
+	if (argc != 2) {
+		return -EINVAL;
+	}
+
+	if ((ret = get_device_info(argv[1], &device)) != 0) {
+		goto out;
+	}
+
+	if (strncmp("nfs", device.fstype, 3) != 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	info("Setting %s readahead to 128\n", device.mountpoint);
+
 	printf("%d\n", readahead);
+
+out:
+	free_device_info(&device);
+	return ret;
 }
-- 
2.35.1