Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 6 Dec 2001 10:20:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 6 Dec 2001 10:20:05 -0500 Received: from smtpde02.sap-ag.de ([194.39.131.53]:3316 "EHLO smtpde02.sap-ag.de") by vger.kernel.org with ESMTP id ; Thu, 6 Dec 2001 10:19:55 -0500 From: Christoph Rohland To: Marcelo Tosatti Cc: lkml Subject: Re: Linux 2.4.17-pre3 In-Reply-To: Organisation: SAP LinuxLab Date: 06 Dec 2001 16:16:23 +0100 In-Reply-To: Message-ID: Lines: 220 User-Agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.1 (Cuyahoga Valley) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SAP: out X-SAP: out Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi Marcelo, On Wed, 5 Dec 2001, Marcelo Tosatti wrote: > pre3: > > - Enable ppro errata workaround (Dave Jones) > - Update tmpfs documentation (Christoph Rohland) Unfortunately the file Documentation/filesystem/tmpfs.txt did not make it into your patch. Here it comes again (slightly modified) Further on the documentation drew some attention to the completeness of the mount option set and I added a uid and gid option. It was easier than adding a TODO entry ;-) And I made the error messages somewhat better understandable from a user perspective. Please apply Christoph diff -uNr 17-pre4/Documentation/filesystems/tmpfs.txt m17-pre4/Documentation/filesystems/tmpfs.txt --- 17-pre4/Documentation/filesystems/tmpfs.txt Thu Jan 1 01:00:00 1970 +++ m17-pre4/Documentation/filesystems/tmpfs.txt Thu Dec 6 16:09:49 2001 @@ -0,0 +1,102 @@ +Tmpfs is a file system which keeps all files in virtual memory. + + +Everything in tmpfs is temporary in the sense that no files will be +created on your hard drive. If you unmount a tmpfs instance, +everything stored therein is lost. + +tmpfs puts everything into the kernel internal caches and grows and +shrinks to accommodate the files it contains and is able to swap +unneeded pages out to swap space. It has maximum size limits which can +be adjusted on the fly via 'mount -o remount ...' + +If you compare it to ramfs (which was the template to create tmpfs) +you gain swapping and limit checking. Another similar thing is the RAM +disk (/dev/ram*), which simulates a fixed size hard disk in physical +RAM, where you have to create an ordinary filesystem on top. Ramdisks +cannot swap and you do not have the possibility to resize them. + +Since tmpfs lives completely in the page cache and on swap, all tmpfs +pages currently in memory will show up as cached. It will not show up +as shared or something like that. Further on you can check the actual +RAM+swap use of a tmpfs instance with df(1) and du(1). + + +tmpfs has the following uses: + +1) There is always a kernel internal mount which you will not see at + all. This is used for shared anonymous mappings and SYSV shared + memory. + + This mount does not depend on CONFIG_TMPFS. If CONFIG_TMPFS is not + set, the user visible part of tmpfs is not build. But the internal + mechanisms are always present. + +2) glibc 2.2 and above expects tmpfs to be mounted at /dev/shm for + POSIX shared memory (shm_open, shm_unlink). Adding the following + line to /etc/fstab should take care of this: + + tmpfs /dev/shm tmpfs defaults 0 0 + + Remember to create the directory that you intend to mount tmpfs on + if necessary (/dev/shm is automagically created if you use devfs). + + This mount is _not_ needed for SYSV shared memory. The internal + mount is used for that. (In the 2.3 kernel versions it was + necessary to mount the predecessor of tmpfs (shm fs) to use SYSV + shared memory) + +3) Some people (including me) find it very convenient to mount it + e.g. on /tmp and /var/tmp and have a big swap partition. But be + aware: loop mounts of tmpfs files do not work due to the internal + design. So mkinitrd shipped by most distributions will fail with a + tmpfs /tmp. + +4) And probably a lot more I do not know about :-) + + +tmpfs has a couple of mount options: + +size: The limit of allocated bytes for this tmpfs instance. The + default is half of your physical RAM without swap. If you + oversize your tmpfs instances the machine will deadlock + since the OOM handler will not be able to free that memory. +nr_blocks: The same as size, but in blocks of PAGECACHE_SIZE. +nr_inodes: The maximum number of inodes for this instance. The default + is half of the number of your physical RAM pages. + +These parameters accept a suffix k, m or g for kilo, mega and giga and +can be changed on remount. + +To specify the initial root directory you can use the following mount +options: + +mode: The permissions as an octal number +uid: The user id +gid: The group id + +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. + + +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. + + +TODOs: + +1) give the size option a percent semantic: If you give a mount option + size=50% the tmpfs instance should be able to grow to 50 percent of + RAM + swap. So the instance should adapt automatically if you add + or remove swap space. +2) loop mounts: This is difficult since loop.c relies on the readpage + operation. This operation gets a page from the caller to be filled + with the content of the file at that position. But tmpfs always has + the page and thus cannot copy the content to the given page. So it + cannot provide this operation. The VM had to be changed seriously + to achieve this. +3) Show the number of tmpfs RAM pages. (As shared?) + +Author: + Christoph Rohland , 1.12.01 diff -uNr 17-pre4/mm/shmem.c m17-pre4/mm/shmem.c --- 17-pre4/mm/shmem.c Mon Nov 26 16:21:58 2001 +++ m17-pre4/mm/shmem.c Thu Dec 6 16:08:26 2001 @@ -1193,7 +1193,7 @@ follow_link: shmem_follow_link, }; -static int shmem_parse_options(char *options, int *mode, unsigned long * blocks, unsigned long *inodes) +static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid, unsigned long * blocks, unsigned long *inodes) { char *this_char, *value, *rest; @@ -1205,7 +1205,7 @@ *value++ = 0; } else { printk(KERN_ERR - "shmem_parse_options: No value for option '%s'\n", + "tmpfs: No value for mount option '%s'\n", this_char); return 1; } @@ -1230,8 +1230,20 @@ *mode = simple_strtoul(value,&rest,8); if (*rest) goto bad_val; + } else if (!strcmp(this_char,"uid")) { + if (!uid) + continue; + *uid = simple_strtoul(value,&rest,0); + if (*rest) + goto bad_val; + } else if (!strcmp(this_char,"gid")) { + if (!gid) + continue; + *gid = simple_strtoul(value,&rest,0); + if (*rest) + goto bad_val; } else { - printk(KERN_ERR "shmem_parse_options: Bad option %s\n", + printk(KERN_ERR "tmpfs: Bad mount option %s\n", this_char); return 1; } @@ -1239,7 +1251,7 @@ return 0; bad_val: - printk(KERN_ERR "shmem_parse_options: Bad value '%s' for option '%s'\n", + printk(KERN_ERR "tmpfs: Bad value '%s' for mount option '%s'\n", value, this_char); return 1; @@ -1251,7 +1263,7 @@ unsigned long max_blocks = sbinfo->max_blocks; unsigned long max_inodes = sbinfo->max_inodes; - if (shmem_parse_options (data, NULL, &max_blocks, &max_inodes)) + if (shmem_parse_options (data, NULL, NULL, NULL, &max_blocks, &max_inodes)) return -EINVAL; return shmem_set_size(sbinfo, max_blocks, max_inodes); } @@ -1268,6 +1280,8 @@ struct dentry * root; unsigned long blocks, inodes; int mode = S_IRWXUGO | S_ISVTX; + uid_t uid = current->fsuid; + gid_t gid = current->fsgid; struct shmem_sb_info *sbinfo = SHMEM_SB(sb); struct sysinfo si; @@ -1279,10 +1293,8 @@ blocks = inodes = si.totalram / 2; #ifdef CONFIG_TMPFS - if (shmem_parse_options (data, &mode, &blocks, &inodes)) { - printk(KERN_ERR "tmpfs invalid option\n"); + if (shmem_parse_options (data, &mode, &uid, &gid, &blocks, &inodes)) return NULL; - } #endif spin_lock_init (&sbinfo->stat_lock); @@ -1299,6 +1311,8 @@ if (!inode) return NULL; + inode->i_uid = uid; + inode->i_gid = gid; root = d_alloc_root(inode); if (!root) { iput(inode); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/