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Subject[PATCH v4 2/2] 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.

Signed-off-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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>
Cc: linux-mm@kvack.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com
---
Documentation/filesystems/tmpfs.txt | 11 +++++
fs/Kconfig | 15 +++++++
include/linux/shmem_fs.h | 1 +
mm/shmem.c | 66 ++++++++++++++++++++++++++++-
4 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/tmpfs.txt b/Documentation/filesystems/tmpfs.txt
index 5ecbc03e6b2f..203e12a684c9 100644
--- a/Documentation/filesystems/tmpfs.txt
+++ b/Documentation/filesystems/tmpfs.txt
@@ -136,6 +136,15 @@ These options do not have any effect on remount. You can change these
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 64-bit, the default is set by CONFIG_TMPFS_INODE64. On 32-bit, inode64 is
+not legal and will produce an error at mount time.
+
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.
@@ -147,3 +156,5 @@ Updated:
Hugh Dickins, 4 June 2007
Updated:
KOSAKI Motohiro, 16 Mar 2010
+Updated:
+ Chris Down, 2 Jan 2020
diff --git a/fs/Kconfig b/fs/Kconfig
index 7b623e9fc1b0..e74f127df22a 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -199,6 +199,21 @@ 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, similarly to the
+ inode64 mount option.
+
+ To override this default, use the inode32 or inode64 mount options.
+
+ If unsure, say N.
+
config HUGETLBFS
bool "HugeTLB file system support"
depends on X86 || IA64 || SPARC64 || (S390 && 64BIT) || \
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 7fac91f490dc..8925eb774518 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -35,6 +35,7 @@ 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 */
struct mempolicy *mpol; /* default memory policy for mappings */
spinlock_t shrinklist_lock; /* Protects shrinklist */
diff --git a/mm/shmem.c b/mm/shmem.c
index 9e97ba972225..05de65112bed 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -115,11 +115,13 @@ 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
@@ -2261,15 +2263,24 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
* since max_inodes is always 0, and is called from
* potentially unknown contexts. As such, use the global
* allocator which doesn't require the per-sb stat_lock.
+ *
+ * No special behaviour is needed for
+ * sbinfo->full_inums, because it's not possible to
+ * manually set on callers of this type, and
+ * CONFIG_TMPFS_INODE64 only applies to user-visible
+ * mounts.
*/
inode->i_ino = get_next_ino();
} else {
spin_lock(&sbinfo->stat_lock);
- if (unlikely(sbinfo->next_ino > UINT_MAX)) {
+ if (unlikely(!sbinfo->full_inums &&
+ sbinfo->next_ino > UINT_MAX)) {
/*
* Emulate get_next_ino uint wraparound for
* compatibility
*/
+ pr_warn("%s: inode number overflow on device %d, consider using inode64 mount option\n",
+ __func__, MINOR(sb->s_dev));
sbinfo->next_ino = 1;
}
inode->i_ino = sbinfo->next_ino++;
@@ -3406,6 +3417,8 @@ enum shmem_param {
Opt_nr_inodes,
Opt_size,
Opt_uid,
+ Opt_inode32,
+ Opt_inode64,
};

static const struct fs_parameter_spec shmem_param_specs[] = {
@@ -3417,6 +3430,8 @@ static const struct fs_parameter_spec shmem_param_specs[] = {
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),
{}
};

@@ -3441,6 +3456,7 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
unsigned long long size;
char *rest;
int opt;
+ const char *err;

opt = fs_parse(fc, &shmem_fs_parameters, param, &result);
if (opt < 0)
@@ -3502,6 +3518,18 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
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) {
+ err = "Cannot use inode64 with <64bit inums in kernel";
+ goto err_msg;
+ }
+ ctx->full_inums = true;
+ ctx->seen |= SHMEM_SEEN_INUMS;
+ break;
}
return 0;

@@ -3509,6 +3537,8 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
return invalf(fc, "tmpfs: Unsupported parameter '%s'", param->key);
bad_value:
return invalf(fc, "tmpfs: Bad value for '%s'", param->key);
+err_msg:
+ return invalf(fc, "tmpfs: %s", err);
}

static int shmem_parse_options(struct fs_context *fc, void *data)
@@ -3593,8 +3623,16 @@ static int shmem_reconfigure(struct fs_context *fc)
}
}

+ 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) {
@@ -3634,6 +3672,29 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
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_HUGE_PAGECACHE
/* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
if (sbinfo->huge)
@@ -3681,6 +3742,8 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
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;
}
@@ -3694,6 +3757,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes;
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;
--
2.24.1
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