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-rw-r--r--Documentation/filesystems/tmpfs.rst18
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
index 4e95929301a5..c44f8b1d3cab 100644
--- a/Documentation/filesystems/tmpfs.rst
+++ b/Documentation/filesystems/tmpfs.rst
@@ -150,6 +150,22 @@ 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 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 accessible by root.
Hugh Dickins, 4 June 2007
:Updated:
KOSAKI Motohiro, 16 Mar 2010
+:Updated:
+ Chris Down, 13 July 2020