linux-kernel - [PATCH] tools/vm/slabinfo: indicates the cause of the EACCES error

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Date:   Tue,  8 Nov 2022 20:47:57 +0800
From:   Rong Tao <rtoax@...mail.com>
To:     akpm@...ux-foundation.org
Cc:     Rong Tao <rongtao@...tc.cn>, Vlastimil Babka <vbabka@...e.cz>,
        Stéphane Graber <stgraber@...ntu.com>,
        Yuanzheng Song <songyuanzheng@...wei.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] tools/vm/slabinfo: indicates the cause of the EACCES error

From: Rong Tao <rongtao@...tc.cn>

If you don't run slabinfo with a superuser, return 0 when read_slab_dir()
reads get_obj_and_str("slabs", &t), because fopen() fails (sometimes
EACCES), causing slabcache() to return directly, without any error during
this time, we should tell the user about the EACCES problem instead of
running successfully($?=0) without any error printing.

 For example:
 $ ./slabinfo
 Permission denied, Try using superuser  <== What this submission did
 $ sudo ./slabinfo
 Name            Objects Objsize   Space Slabs/Part/Cpu  O/S O %Fr %Ef Flg
 Acpi-Namespace     5950      48  286.7K         65/0/5   85 0   0  99
 Acpi-Operand      13664      72  999.4K       231/0/13   56 0   0  98
 ...

Signed-off-by: Rong Tao <rongtao@...tc.cn>
---
 tools/vm/slabinfo.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index 0fffaeedee76..cfaeaea71042 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -157,9 +157,11 @@ static unsigned long read_obj(const char *name)
 {
 	FILE *f = fopen(name, "r");
 
-	if (!f)
+	if (!f) {
 		buffer[0] = 0;
-	else {
+		if (errno == EACCES)
+			fatal("%s, Try using superuser\n", strerror(errno));
+	} else {
 		if (!fgets(buffer, sizeof(buffer), f))
 			buffer[0] = 0;
 		fclose(f);
-- 
2.31.1