[patch 060/163] tmpfs: support 64-bit inums per-sb

Andrew Morton
2020-08-07T06:20:29Z

From: Chris Down <chris@chrisdown.name>
Subject: tmpfs: support 64-bit inums per-sb

The default is still set to inode32 for backwards compatibility, but
system administrators can opt in to the new 64-bit inode numbers by
either:

1. Passing inode64 on the command line when mounting, or
2. Configuring the kernel with CONFIG_TMPFS_INODE64=y

The inode64 and inode32 names are used based on existing precedent from
XFS.

[hughd@google.com: Kconfig fixes]
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008011928010.13320@eggly.anvils
Link: http://lkml.kernel.org/r/8b23758d0c66b5e2263e08baf9c4b6a7565cbd8f.1594661218.git.chris@chrisdown.name
Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

Documentation/filesystems/tmpfs.rst | 18 +++++++
fs/Kconfig | 21 ++++++++
include/linux/shmem_fs.h | 1
mm/shmem.c | 65 +++++++++++++++++++++++++-
4 files changed, 103 insertions(+), 2 deletions(-)

--- a/Documentation/filesystems/tmpfs.rst~tmpfs-support-64-bit-inums-per-sb
+++ a/Documentation/filesystems/tmpfs.rst
@@ -150,6 +150,22 @@ These options do not have any effect on
parameters with chmod(1), chown(1) and chgrp(1) on a mounted filesystem.

+tmpfs has a mount option to select whether it will wrap at 32- or 64-bit inode
+numbers:
+
+======= ========================
+inode64 Use 64-bit inode numbers
+inode32 Use 32-bit inode numbers
+======= ========================
+
+On a 32-bit kernel, inode32 is implicit, and inode64 is refused at mount time.
+On a 64-bit kernel, CONFIG_TMPFS_INODE64 sets the default. inode64 avoids the
+possibility of multiple files with the same inode number on a single device;
+but risks glibc failing with EOVERFLOW once 33-bit inode numbers are reached -
+if a long-lived tmpfs is accessed by 32-bit applications so ancient that
+opening a file larger than 2GiB fails with EINVAL.
+
+
So 'mount -t tmpfs -o size=10G,nr_inodes=10k,mode=700 tmpfs /mytmpfs'
will give you tmpfs instance on /mytmpfs which can allocate 10GB
RAM/SWAP in 10240 inodes and it is only accessible by root.
@@ -161,3 +177,5 @@ RAM/SWAP in 10240 inodes and it is only
Hugh Dickins, 4 June 2007
:Updated:
KOSAKI Motohiro, 16 Mar 2010
+:Updated:
+ Chris Down, 13 July 2020
--- a/fs/Kconfig~tmpfs-support-64-bit-inums-per-sb
+++ a/fs/Kconfig
@@ -201,6 +201,27 @@ config TMPFS_XATTR

If unsure, say N.

+config TMPFS_INODE64
+ bool "Use 64-bit ino_t by default in tmpfs"
+ depends on TMPFS && 64BIT
+ default n
+ help
+ tmpfs has historically used only inode numbers as wide as an unsigned
+ int. In some cases this can cause wraparound, potentially resulting
+ in multiple files with the same inode number on a single device. This
+ option makes tmpfs use the full width of ino_t by default, without
+ needing to specify the inode64 option when mounting.
+
+ But if a long-lived tmpfs is to be accessed by 32-bit applications so
+ ancient that opening a file larger than 2GiB fails with EINVAL, then
+ the INODE64 config option and inode64 mount option risk operations
+ failing with EOVERFLOW once 33-bit inode numbers are reached.
+
+ To override this configured default, use the inode32 or inode64
+ option when mounting.
+
+ If unsure, say N.
+
config HUGETLBFS
bool "HugeTLB file system support"
depends on X86 || IA64 || SPARC64 || (S390 && 64BIT) || \
--- a/include/linux/shmem_fs.h~tmpfs-support-64-bit-inums-per-sb
+++ a/include/linux/shmem_fs.h
@@ -36,6 +36,7 @@ struct shmem_sb_info {
unsigned char huge; /* Whether to try for hugepages */
kuid_t uid; /* Mount uid for root directory */
kgid_t gid; /* Mount gid for root directory */
+ bool full_inums; /* If i_ino should be uint or ino_t */
ino_t next_ino; /* The next per-sb inode number to use */
ino_t __percpu *ino_batch; /* The next per-cpu inode number to use */
struct mempolicy *mpol; /* default memory policy for mappings */
--- a/mm/shmem.c~tmpfs-support-64-bit-inums-per-sb
+++ a/mm/shmem.c
@@ -114,11 +114,13 @@ struct shmem_options {
kuid_t uid;
kgid_t gid;
umode_t mode;
+ bool full_inums;
int huge;
int seen;
#define SHMEM_SEEN_BLOCKS 1
#define SHMEM_SEEN_INODES 2
#define SHMEM_SEEN_HUGE 4
+#define SHMEM_SEEN_INUMS 8
};

#ifdef CONFIG_TMPFS
@@ -286,12 +288,17 @@ static int shmem_reserve_inode(struct su
ino = sbinfo->next_ino++;
if (unlikely(is_zero_ino(ino)))
ino = sbinfo->next_ino++;
- if (unlikely(ino > UINT_MAX)) {
+ if (unlikely(!sbinfo->full_inums &&
+ ino > UINT_MAX)) {
/*
* Emulate get_next_ino uint wraparound for
* compatibility
*/
- ino = 1;
+ if (IS_ENABLED(CONFIG_64BIT))
+ pr_warn("%s: inode number overflow on device %d, consider using inode64 mount option\n",
+ __func__, MINOR(sb->s_dev));
+ sbinfo->next_ino = 1;
+ ino = sbinfo->next_ino++;
}
*inop = ino;
}
@@ -304,6 +311,10 @@ static int shmem_reserve_inode(struct su
* unknown contexts. As such, use a per-cpu batched allocator
* which doesn't require the per-sb stat_lock unless we are at
* the batch boundary.
+ *
+ * We don't need to worry about inode{32,64} since SB_KERNMOUNT
+ * shmem mounts are not exposed to userspace, so we don't need
+ * to worry about things like glibc compatibility.
*/
ino_t *next_ino;
next_ino = per_cpu_ptr(sbinfo->ino_batch, get_cpu());
@@ -3397,6 +3408,8 @@ enum shmem_param {
Opt_nr_inodes,
Opt_size,
Opt_uid,
+ Opt_inode32,
+ Opt_inode64,
};

static const struct constant_table shmem_param_enums_huge[] = {
@@ -3416,6 +3429,8 @@ const struct fs_parameter_spec shmem_fs_
fsparam_string("nr_inodes", Opt_nr_inodes),
fsparam_string("size", Opt_size),
fsparam_u32 ("uid", Opt_uid),
+ fsparam_flag ("inode32", Opt_inode32),
+ fsparam_flag ("inode64", Opt_inode64),
{}
};

@@ -3487,6 +3502,18 @@ static int shmem_parse_one(struct fs_con
break;
}
goto unsupported_parameter;
+ case Opt_inode32:
+ ctx->full_inums = false;
+ ctx->seen |= SHMEM_SEEN_INUMS;
+ break;
+ case Opt_inode64:
+ if (sizeof(ino_t) < 8) {
+ return invalfc(fc,
+ "Cannot use inode64 with <64bit inums in kernel\n");
+ }
+ ctx->full_inums = true;
+ ctx->seen |= SHMEM_SEEN_INUMS;
+ break;
}
return 0;

@@ -3578,8 +3605,16 @@ static int shmem_reconfigure(struct fs_c
}
}

+ if ((ctx->seen & SHMEM_SEEN_INUMS) && !ctx->full_inums &&
+ sbinfo->next_ino > UINT_MAX) {
+ err = "Current inum too high to switch to 32-bit inums";
+ goto out;
+ }
+
if (ctx->seen & SHMEM_SEEN_HUGE)
sbinfo->huge = ctx->huge;
+ if (ctx->seen & SHMEM_SEEN_INUMS)
+ sbinfo->full_inums = ctx->full_inums;
if (ctx->seen & SHMEM_SEEN_BLOCKS)
sbinfo->max_blocks = ctx->blocks;
if (ctx->seen & SHMEM_SEEN_INODES) {
@@ -3619,6 +3654,29 @@ static int shmem_show_options(struct seq
if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u",
from_kgid_munged(&init_user_ns, sbinfo->gid));
+
+ /*
+ * Showing inode{64,32} might be useful even if it's the system default,
+ * since then people don't have to resort to checking both here and
+ * /proc/config.gz to confirm 64-bit inums were successfully applied
+ * (which may not even exist if IKCONFIG_PROC isn't enabled).
+ *
+ * We hide it when inode64 isn't the default and we are using 32-bit
+ * inodes, since that probably just means the feature isn't even under
+ * consideration.
+ *
+ * As such:
+ *
+ * +-----------------+-----------------+
+ * | TMPFS_INODE64=y | TMPFS_INODE64=n |
+ * +------------------+-----------------+-----------------+
+ * | full_inums=true | show | show |
+ * | full_inums=false | show | hide |
+ * +------------------+-----------------+-----------------+
+ *
+ */
+ if (IS_ENABLED(CONFIG_TMPFS_INODE64) || sbinfo->full_inums)
+ seq_printf(seq, ",inode%d", (sbinfo->full_inums ? 64 : 32));
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
if (sbinfo->huge)
@@ -3667,6 +3725,8 @@ static int shmem_fill_super(struct super
ctx->blocks = shmem_default_max_blocks();
if (!(ctx->seen & SHMEM_SEEN_INODES))
ctx->inodes = shmem_default_max_inodes();
+ if (!(ctx->seen & SHMEM_SEEN_INUMS))
+ ctx->full_inums = IS_ENABLED(CONFIG_TMPFS_INODE64);
} else {
sb->s_flags |= SB_NOUSER;
}
@@ -3684,6 +3744,7 @@ static int shmem_fill_super(struct super
}
sbinfo->uid = ctx->uid;
sbinfo->gid = ctx->gid;
+ sbinfo->full_inums = ctx->full_inums;
sbinfo->mode = ctx->mode;
sbinfo->huge = ctx->huge;
sbinfo->mpol = ctx->mpol;
_