diff options
Diffstat (limited to 'hurd')
| -rw-r--r-- | hurd/translator.mdwn | 1 | ||||
| -rw-r--r-- | hurd/translator/mtab.mdwn | 23 | ||||
| -rw-r--r-- | hurd/translator/mtab/discussion.mdwn | 145 | ||||
| -rw-r--r-- | hurd/translator/procfs/jkoenig/discussion.mdwn | 4 |
4 files changed, 172 insertions, 1 deletions
diff --git a/hurd/translator.mdwn b/hurd/translator.mdwn index d4eaf950..f1c07bde 100644 --- a/hurd/translator.mdwn +++ b/hurd/translator.mdwn @@ -97,6 +97,7 @@ The [[concept|concepts]] of translators creates its own problems, too: * [[ext2fs]] * [[fatfs]] * [[magic]] +* [[mtab]] * [[unionfs]] * [[nfs]] * [[symlink]] diff --git a/hurd/translator/mtab.mdwn b/hurd/translator/mtab.mdwn new file mode 100644 index 00000000..8eca15b9 --- /dev/null +++ b/hurd/translator/mtab.mdwn @@ -0,0 +1,23 @@ +[[!meta copyright="Copyright © 2008, 2009, 2013 Free Software Foundation, +Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +In traditional monolithic system, the kernel keeps track of all mounts; the +information is available through `/proc/mounts` (on Linux at least), and in a +very similar form in `/etc/mtab`. + +The Hurd on the other hand has a totally +[[decentralized_file_system|hurd/virtual_file_system]]. There is no single +entity involved in all mounts. Rather, only the parent file system to which a +mountpoint ([[hurd/translator]]) is attached is involved. As a result, there +is no central place keeping track of mounts. + +The `mtab` translator has been implemented; see the [[discussion]] subpage for +design considerations. diff --git a/hurd/translator/mtab/discussion.mdwn b/hurd/translator/mtab/discussion.mdwn new file mode 100644 index 00000000..ca6a86fd --- /dev/null +++ b/hurd/translator/mtab/discussion.mdwn @@ -0,0 +1,145 @@ +[[!meta copyright="Copyright © 2008, 2009, 2013 Free Software Foundation, +Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_documentation]] The following text needs to be updated. + +# Original Project Description + +As a consequence, there is currently no easy way to obtain a listing of all +mounted file systems. This also means that commands like `df` can only work on +explicitly specified mountpoints, instead of displaying the usual listing. + +One possible solution to this would be for the translator startup mechanism to +update the `mtab` on any `mount`/`unmount`, like in traditional systems. +However, there are some problems with this approach. Most notably: what to do +with passive translators, i.e., translators that are not presently running, but +set up to be started automatically whenever the node is accessed? Probably +these should be counted among the mounted filesystems; but how to handle the +`mtab` updates for a translator that is not started yet? Generally, being +centralized and event-based, this is a pretty inelegant, non-hurdish solution. + +A more promising approach is to have `mtab` exported by a special translator, +which gathers the necessary information on demand. This could work by +traversing the tree of translators, asking each one for mount points attached +to it. (Theoretically, it could also be done by just traversing *all* nodes, +checking each one for attached translators. That would be very inefficient, +though. Thus a special interface is probably required, that allows asking a +translator to list mount points only.) + +There are also some other issues to keep in mind. Traversing arbitrary +translators set by other users can be quite dangerous -- and it's probably not +very interesting anyways what private filesystems some other user has mounted. +But what about the global `/etc/mtab`? Should it list only root-owned +filesystems? Or should it create different listings depending on what user +contacts it?... + +That leads to a more generic question: which translators should be actually +listed? There are different kinds of translators: ranging from traditional +filesystems ([[disks|hurd/libdiskfs]] and other actual +[[stores|hurd/translator/storeio]]), but also purely virtual filesystems like +[[hurd/translator/ftpfs]] or [[hurd/translator/unionfs]], and even things that +have very little to do with a traditional filesystem, like a +[[gzip_translator|hurd/translator/storeio]], +[[mbox_translator|hurd/translator/mboxfs]], +[[xml_translator|hurd/translator/xmlfs]], or various device file translators... +Listing all of these in `/etc/mtab` would be pretty pointless, so some kind of +classification mechanism is necessary. By default it probably should list only +translators that claim to be real filesystems, though alternative views with +other filtering rules might be desirable. + +After taking decisions on the outstanding design questions, the student will +implement both the actual mtab translator, and the +necessary interface(s) for gathering the data. It requires getting a good +understanding of the translator mechanism and Hurd interfaces in general. + + +# IRC, freenode, #hurd, 2013-04-17 + + <kuldeepdhaka> thinking how to get the listing. traversing would be + ineffecient, trying to come up with something better + <braunr> what listing ? + <braunr> and traversing what ? + <kuldeepdhaka> mtab + <braunr> well i assumed so + <braunr> be more precise please + <kuldeepdhaka> when the translator is done initalized <translation + info> are written to /etc/mtab <translation info> will be provided + by the translator, and when some one want to read the info just read it + this way if their is some credentials like ftp sites pass username can be + masked by the translator + <kuldeepdhaka> if some trans dont want to list them, no need to write to + file | while unmounting (sorry i couldnt find the right word) , it + will pass the mount node address | <translation info> will have special + structure to remove/add mounts example "a /mount-to /mount-from" = add + , "r /mount-to" = remove here "/mount-to" will be unique for every + mount + <kuldeepdhaka> this have a draw back , we would have to trust trans for the + listed data | also "/mount-to" + "/mount-from" could be used a + combination for making sure that other trans unable remove others trans + mount data + <kuldeepdhaka> sorry but "also "/mount-to" + "/mount-from" could be used a + combination for making sure that other trans unable remove others trans + mount data" this is a bad idea if we had to print the whole thing + <kuldeepdhaka> braunr, whats ur opinion? + <pinotree> you don't need a mtab to "unmount" things on hurd + <braunr> kuldeepdhaka: hum, have you read the project idea ? + <braunr> + http://darnassus.sceen.net/~hurd-web/community/gsoc/project_ideas/mtab/ + <braunr> A more promising approach is to have mtab exported by a special + translator, which gathers the necessary information on demand. This could + work by traversing the tree of translators, asking each one for mount + points attached to it. + <kuldeepdhaka> pinotree, not to unmount, i mean is to remove the + <translation data> + <braunr> for a first implementation, i'd suggest a recursive traversal of + root-owned translators + <kuldeepdhaka> braunr, hum, but it did stated it as inefficient + <braunr> where ? + <kuldeepdhaka> para 5 , line 3 + <kuldeepdhaka> and line 6 + <braunr> no + <braunr> traversing "all" nodes would be inefficient + <braunr> translators which host the nodes of other translators could + maintain a simple list of active translators + <braunr> ext2fs, e.g. (if that's not already the case) could keep the list + of the translators it started + <braunr> we can already see that list with pstree for example + <braunr> but this new list would only retain those relevant for mtab + <braunr> i.e. root-owned ones + <pinotree> i would not limit to those though + <braunr> and then filter on their type (e.g. file system ones) + <braunr> pinotree: why ? + <pinotree> this way you could have proper per-user /proc/$pid/mounts info + <braunr> we could also very easily have a denial of service + <kuldeepdhaka> but how will the mount point and source point will be + listed? + <braunr> they're returned by the translator + <kuldeepdhaka> k + <braunr> you ask /, it returns its store and its options, and asks its + children recursively + <braunr> a /home translator would return its store and its options + <braunr> etc.. + <braunr> each translator would build the complete path before returning it + <braunr> sort of, it's very basic + <braunr> but that would be a very hurdish way to do it + <kuldeepdhaka> shall /etc/mtab should be made seek-able and what should be + the filesize? content are generated on demand so, it could arise problem + (fsize:0 , seek-able:no), ur opinions? + <braunr> kuldeepdhaka: it should have all the properties of a regular file + <braunr> the filesize would be determined after it's generated + <braunr> being empty doesn't imply it's not seekable + <kuldeepdhaka> content is generated on demand so, could cause problem while + seeking and filesize, shall i still program as regular file? + <kuldeepdhaka> in two different read, it could generate different content, + though same seek pos is used... + <braunr> what ? + <braunr> the content is generated on open + <kuldeepdhaka> ooh, ok diff --git a/hurd/translator/procfs/jkoenig/discussion.mdwn b/hurd/translator/procfs/jkoenig/discussion.mdwn index d26f05f9..b5517b90 100644 --- a/hurd/translator/procfs/jkoenig/discussion.mdwn +++ b/hurd/translator/procfs/jkoenig/discussion.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2010, 2011, 2012 Free Software Foundation, +[[!meta copyright="Copyright © 2010, 2011, 2012, 2013 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable @@ -206,6 +206,8 @@ IRC, freenode, #hurd, 2011-07-25 i don't remember) < pinotree> not a strict need +A [[mtab]] translator now exists. + # `/proc/[PID]/auxv`, `/proc/[PID]/exe`, `/proc/[PID]/mem` |