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Wong" , linux-fsdevel@vger.kernel.org Subject: [PATCH 2/2] ext4: Fix reserved gdt blocks handling in fsmap Date: Tue, 5 Aug 2025 14:00:31 +0530 Message-ID: <08781b796453a5770112aa96ad14c864fbf31935.1754377641.git.ojaswin@linux.ibm.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: NFRd-Gjr_vjarIkfFH4KIKBQLQWtTu-R X-Proofpoint-ORIG-GUID: 8XyL0S1Qd62oFcULz-cTKEb1QYwmJXrY X-Authority-Analysis: v=2.4 cv=GNoIEvNK c=1 sm=1 tr=0 ts=6891c12f cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=2OwXVqhp2XgA:10 a=VnNF1IyMAAAA:8 a=GBxxKAqwAsD-tcH_wUcA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODA1MDA2MCBTYWx0ZWRfX2c+NSAkHFWjZ LQXVkWFjSMXcpp4U6inrCBId3jThU/3LjvGg9D1T4sFKbB/TclBFgguvKSmlQNZ4I6oUNTQwBRc ex9psnliGKAL8T6i8yYcMYCvq7oZ1Al/1H4ypumUuGgzExF8IIeOWJZ75+g151KJHhNWmFwoWql 6ECBz7SDl07h1qmLw6Euc4J7jmFczMwAiCfr0JgPlSv5PpkUnUM4Ejfwwgz1IzstnirFS2ffIRZ EFS/2z+K6RxtCbA4w52xqpbq7beECPsg24o1Y+ZKrtH+u+rTOcuag9bqDlbBhNzw1dtyvnTaQSd A9F5sKFXfmQ65gyHIBbR97o7nNmC/Gpp/Yg2zzXkHpK+b+9bOQB9BAeU4bm0ftYh7HGt3MFfi+n wlLt0SrvqH6KvGioX0t7H59bzPq1xvjpjX6TYHYur7XZAF2AFbCN6p7I3a1UQ5TQJsg6LAV9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-05_02,2025-08-04_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 phishscore=0 adultscore=0 spamscore=0 bulkscore=0 mlxscore=0 mlxlogscore=999 impostorscore=0 priorityscore=1501 suspectscore=0 lowpriorityscore=0 clxscore=1015 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2508050060 In some cases like small FSes with no meta_bg and where the resize doesn't need extra gdt blocks as it can fit in the current one, s_reserved_gdt_blocks is set as 0, which causes fsmap to emit a 0 length entry, which is incorrect. $ mkfs.ext4 -b 65536 -O bigalloc /dev/sda 5G $ mount /dev/sda /mnt/scratch $ xfs_io -c "fsmap -d" /mnt/scartch 0: 253:48 [0..127]: static fs metadata 128 1: 253:48 [128..255]: special 102:1 128 2: 253:48 [256..255]: special 102:2 0 <---- 0 len entry 3: 253:48 [256..383]: special 102:3 128 Fix this by adding a check for this case. Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls") Signed-off-by: Ojaswin Mujoo --- fs/ext4/fsmap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c index 9d63c39f6077..91185c40f755 100644 --- a/fs/ext4/fsmap.c +++ b/fs/ext4/fsmap.c @@ -393,6 +393,14 @@ static unsigned int ext4_getfsmap_find_sb(struct super_block *sb, /* Reserved GDT blocks */ if (!ext4_has_feature_meta_bg(sb) || metagroup < first_meta_bg) { len = le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks); + + /* + * mkfs.ext4 can set s_reserved_gdt_blocks as 0 in some cases, + * check for that. + */ + if (!len) + return 0; + error = ext4_getfsmap_fill(meta_list, fsb, len, EXT4_FMR_OWN_RESV_GDT); if (error) -- 2.49.0