bus/pci: fix Intel IOMMU sysfs access check

[ upstream commit 2e8d5cf ]

Just open the sysfs file and handle failure, rather than using access().
This eliminates Coverity warnings about TOCTOU
"time of check versus time of use"; although for this sysfs file that is
not really an issue anyway.

Coverity issue: 347276
Fixes: 54a328f ("bus/pci: forbid IOVA mode if IOMMU address width too small")

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: David Marchand <david.marchand@redhat.com>

drivers/bus/pci/linux/pci.c

@@ -592,18 +592,19 @@ pci_one_device_iommu_support_va(struct rte_pci_device *dev)
 		 "%s/" PCI_PRI_FMT "/iommu/intel-iommu/cap",
 		 rte_pci_get_sysfs_path(), addr->domain, addr->bus, addr->devid,
 		 addr->function);
-	if (access(filename, F_OK) == -1) {
-		/* We don't have an Intel IOMMU, assume VA supported*/
-		return true;
-	}
 
-	/* We have an intel IOMMU */
 	fp = fopen(filename, "r");
 	if (fp == NULL) {
-		RTE_LOG(ERR, EAL, "%s(): can't open %s\n", __func__, filename);
+		/* We don't have an Intel IOMMU, assume VA supported */
+		if (errno == ENOENT)
+			return true;
+
+		RTE_LOG(ERR, EAL, "%s(): can't open %s: %s\n",
+			__func__, filename, strerror(errno));
 		return false;
 	}
 
+	/* We have an Intel IOMMU */
 	if (fscanf(fp, "%" PRIx64, &vtd_cap_reg) != 1) {
 		RTE_LOG(ERR, EAL, "%s(): can't read %s\n", __func__, filename);
 		fclose(fp);