diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/00-INDEX | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/9p.txt | 32 | ||||
| -rw-r--r-- | Documentation/filesystems/Exporting | 115 | ||||
| -rw-r--r-- | Documentation/filesystems/Locking | 11 | ||||
| -rw-r--r-- | Documentation/filesystems/ext3.txt | 14 | ||||
| -rw-r--r-- | Documentation/filesystems/files.txt | 6 | ||||
| -rw-r--r-- | Documentation/filesystems/locks.txt | 67 | ||||
| -rw-r--r-- | Documentation/filesystems/mandatory-locking.txt | 171 | ||||
| -rw-r--r-- | Documentation/filesystems/proc.txt | 37 | ||||
| -rw-r--r-- | Documentation/filesystems/quota.txt | 59 | ||||
| -rw-r--r-- | Documentation/filesystems/ramfs-rootfs-initramfs.txt | 14 | ||||
| -rw-r--r-- | Documentation/filesystems/sysfs.txt | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 53 |
13 files changed, 477 insertions, 114 deletions
diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX index 59db1bca702..1de155e2dc3 100644 --- a/Documentation/filesystems/00-INDEX +++ b/Documentation/filesystems/00-INDEX @@ -44,14 +44,24 @@ files.txt - info on file management in the Linux kernel. fuse.txt - info on the Filesystem in User SpacE including mount options. +gfs2.txt + - info on the Global File System 2. hfs.txt - info on the Macintosh HFS Filesystem for Linux. +hfsplus.txt + - info on the Macintosh HFSPlus Filesystem for Linux. hpfs.txt - info and mount options for the OS/2 HPFS. +inotify.txt + - info on the powerful yet simple file change notification system. isofs.txt - info and mount options for the ISO 9660 (CDROM) filesystem. jfs.txt - info and mount options for the JFS filesystem. +locks.txt + - info on file locking implementations, flock() vs. fcntl(), etc. +mandatory-locking.txt + - info on the Linux implementation of Sys V mandatory file locking. ncpfs.txt - info on Novell Netware(tm) filesystem using NCP protocol. ntfs.txt diff --git a/Documentation/filesystems/9p.txt b/Documentation/filesystems/9p.txt index cda6905cbe4..bf8080640eb 100644 --- a/Documentation/filesystems/9p.txt +++ b/Documentation/filesystems/9p.txt @@ -35,17 +35,19 @@ For remote file server: For Plan 9 From User Space applications (http://swtch.com/plan9) - mount -t 9p `namespace`/acme /mnt/9 -o proto=unix,uname=$USER + mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER OPTIONS ======= - proto=name select an alternative transport. Valid options are + trans=name select an alternative transport. Valid options are currently: - unix - specifying a named pipe mount point - tcp - specifying a normal TCP/IP connection - fd - used passed file descriptors for connection + unix - specifying a named pipe mount point + tcp - specifying a normal TCP/IP connection + fd - used passed file descriptors for connection (see rfdno and wfdno) + virtio - connect to the next virtio channel available + (from lguest or KVM with trans_virtio module) uname=name user name to attempt mount as on the remote server. The server may override or ignore this value. Certain user @@ -54,7 +56,7 @@ OPTIONS aname=name aname specifies the file tree to access when the server is offering several exported file systems. - cache=mode specifies a cacheing policy. By default, no caches are used. + cache=mode specifies a caching policy. By default, no caches are used. loose = no attempts are made at consistency, intended for exclusive, read-only mounts @@ -68,9 +70,9 @@ OPTIONS 0x40 = display transport debug 0x80 = display allocation debug - rfdno=n the file descriptor for reading with proto=fd + rfdno=n the file descriptor for reading with trans=fd - wfdno=n the file descriptor for writing with proto=fd + wfdno=n the file descriptor for writing with trans=fd maxdata=n the number of bytes to use for 9p packet payload (msize) @@ -78,9 +80,9 @@ OPTIONS noextend force legacy mode (no 9p2000.u semantics) - uid attempt to mount as a particular uid + dfltuid attempt to mount as a particular uid - gid attempt to mount with a particular gid + dfltgid attempt to mount with a particular gid afid security channel - used by Plan 9 authentication protocols @@ -88,6 +90,16 @@ OPTIONS This can be used to share devices/named pipes/sockets between hosts. This functionality will be expanded in later versions. + access there are three access modes. + user = if a user tries to access a file on v9fs + filesystem for the first time, v9fs sends an + attach command (Tattach) for that user. + This is the default mode. + <uid> = allows only user with uid=<uid> to access + the files on the mounted filesystem + any = v9fs does single attach and performs all + operations as one user + RESOURCES ========= diff --git a/Documentation/filesystems/Exporting b/Documentation/filesystems/Exporting index 31047e0fe14..87019d2b598 100644 --- a/Documentation/filesystems/Exporting +++ b/Documentation/filesystems/Exporting @@ -2,9 +2,12 @@ Making Filesystems Exportable ============================= -Most filesystem operations require a dentry (or two) as a starting +Overview +-------- + +All filesystem operations require a dentry (or two) as a starting point. Local applications have a reference-counted hold on suitable -dentrys via open file descriptors or cwd/root. However remote +dentries via open file descriptors or cwd/root. However remote applications that access a filesystem via a remote filesystem protocol such as NFS may not be able to hold such a reference, and so need a different way to refer to a particular dentry. As the alternative @@ -13,14 +16,14 @@ server-reboot (among other things, though these tend to be the most problematic), there is no simple answer like 'filename'. The mechanism discussed here allows each filesystem implementation to -specify how to generate an opaque (out side of the filesystem) byte +specify how to generate an opaque (outside of the filesystem) byte string for any dentry, and how to find an appropriate dentry for any given opaque byte string. This byte string will be called a "filehandle fragment" as it corresponds to part of an NFS filehandle. A filesystem which supports the mapping between filehandle fragments -and dentrys will be termed "exportable". +and dentries will be termed "exportable". @@ -89,11 +92,9 @@ For a filesystem to be exportable it must: 1/ provide the filehandle fragment routines described below. 2/ make sure that d_splice_alias is used rather than d_add when ->lookup finds an inode for a given parent and name. - Typically the ->lookup routine will end: - if (inode) - return d_splice(inode, dentry); - d_add(dentry, inode); - return NULL; + Typically the ->lookup routine will end with a: + + return d_splice_alias(inode, dentry); } @@ -101,67 +102,39 @@ For a filesystem to be exportable it must: A file system implementation declares that instances of the filesystem are exportable by setting the s_export_op field in the struct super_block. This field must point to a "struct export_operations" -struct which could potentially be full of NULLs, though normally at -least get_parent will be set. - - The primary operations are decode_fh and encode_fh. -decode_fh takes a filehandle fragment and tries to find or create a -dentry for the object referred to by the filehandle. -encode_fh takes a dentry and creates a filehandle fragment which can -later be used to find/create a dentry for the same object. - -decode_fh will probably make use of "find_exported_dentry". -This function lives in the "exportfs" module which a filesystem does -not need unless it is being exported. So rather that calling -find_exported_dentry directly, each filesystem should call it through -the find_exported_dentry pointer in it's export_operations table. -This field is set correctly by the exporting agent (e.g. nfsd) when a -filesystem is exported, and before any export operations are called. - -find_exported_dentry needs three support functions from the -filesystem: - get_name. When given a parent dentry and a child dentry, this - should find a name in the directory identified by the parent - dentry, which leads to the object identified by the child dentry. - If no get_name function is supplied, a default implementation is - provided which uses vfs_readdir to find potential names, and - matches inode numbers to find the correct match. - - get_parent. When given a dentry for a directory, this should return - a dentry for the parent. Quite possibly the parent dentry will - have been allocated by d_alloc_anon. - The default get_parent function just returns an error so any - filehandle lookup that requires finding a parent will fail. - ->lookup("..") is *not* used as a default as it can leave ".." - entries in the dcache which are too messy to work with. - - get_dentry. When given an opaque datum, this should find the - implied object and create a dentry for it (possibly with - d_alloc_anon). - The opaque datum is whatever is passed down by the decode_fh - function, and is often simply a fragment of the filehandle - fragment. - decode_fh passes two datums through find_exported_dentry. One that - should be used to identify the target object, and one that can be - used to identify the object's parent, should that be necessary. - The default get_dentry function assumes that the datum contains an - inode number and a generation number, and it attempts to get the - inode using "iget" and check it's validity by matching the - generation number. A filesystem should only depend on the default - if iget can safely be used this way. - -If decode_fh and/or encode_fh are left as NULL, then default -implementations are used. These defaults are suitable for ext2 and -extremely similar filesystems (like ext3). - -The default encode_fh creates a filehandle fragment from the inode -number and generation number of the target together with the inode -number and generation number of the parent (if the parent is -required). - -The default decode_fh extract the target and parent datums from the -filehandle assuming the format used by the default encode_fh and -passed them to find_exported_dentry. +struct which has the following members: + + encode_fh (optional) + Takes a dentry and creates a filehandle fragment which can later be used + to find or create a dentry for the same object. The default + implementation creates a filehandle fragment that encodes a 32bit inode + and generation number for the inode encoded, and if necessary the + same information for the parent. + + fh_to_dentry (mandatory) + Given a filehandle fragment, this should find the implied object and + create a dentry for it (possibly with d_alloc_anon). + + fh_to_parent (optional but strongly recommended) + Given a filehandle fragment, this should find the parent of the + implied object and create a dentry for it (possibly with d_alloc_anon). + May fail if the filehandle fragment is too small. + + get_parent (optional but strongly recommended) + When given a dentry for a directory, this should return a dentry for + the parent. Quite possibly the parent dentry will have been allocated + by d_alloc_anon. The default get_parent function just returns an error + so any filehandle lookup that requires finding a parent will fail. + ->lookup("..") is *not* used as a default as it can leave ".." entries + in the dcache which are too messy to work with. + + get_name (optional) + When given a parent dentry and a child dentry, this should find a name + in the directory identified by the parent dentry, which leads to the + object identified by the child dentry. If no get_name function is + supplied, a default implementation is provided which uses vfs_readdir + to find potential names, and matches inode numbers to find the correct + match. A filehandle fragment consists of an array of 1 or more 4byte words, @@ -172,5 +145,3 @@ generated by encode_fh, in which case it will have been padded with nuls. Rather, the encode_fh routine should choose a "type" which indicates the decode_fh how much of the filehandle is valid, and how it should be interpreted. - - diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index f0f825808ca..37c10cba717 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -178,15 +178,18 @@ prototypes: locking rules: All except set_page_dirty may block - BKL PageLocked(page) + BKL PageLocked(page) i_sem writepage: no yes, unlocks (see below) readpage: no yes, unlocks sync_page: no maybe writepages: no set_page_dirty no no readpages: no -prepare_write: no yes -commit_write: no yes +prepare_write: no yes yes +commit_write: no yes yes +write_begin: no locks the page yes +write_end: no yes, unlocks yes +perform_write: no n/a yes bmap: yes invalidatepage: no yes releasepage: no yes @@ -221,7 +224,7 @@ against the page the filesystem should redirty the page with redirty_page_for_writepage(), then unlock the page and return zero. This may also be done to avoid internal deadlocks, but rarely. -If the filesytem is called for sync then it must wait on any +If the filesystem is called for sync then it must wait on any in-progress I/O and then start new I/O. The filesystem should unlock the page synchronously, before returning to the diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 4aecc9bdb27..b45f3c1b8b4 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt @@ -130,12 +130,12 @@ Device layer. Journaling Block Device layer ----------------------------- -The Journaling Block Device layer (JBD) isn't ext3 specific. It was design to -add journaling capabilities on a block device. The ext3 filesystem code will -inform the JBD of modifications it is performing (called a transaction). The -journal supports the transactions start and stop, and in case of crash, the -journal can replayed the transactions to put the partition back in a -consistent state fast. +The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed +to add journaling capabilities to a block device. The ext3 filesystem code +will inform the JBD of modifications it is performing (called a transaction). +The journal supports the transactions start and stop, and in case of a crash, +the journal can replay the transactions to quickly put the partition back into +a consistent state. Handles represent a single atomic update to a filesystem. JBD can handle an external journal on a block device. @@ -164,7 +164,7 @@ written to the journal first, and then to its final location. In the event of a crash, the journal can be replayed, bringing both data and metadata into a consistent state. This mode is the slowest except when data needs to be read from and written to disk at the same time where it -outperforms all others modes. +outperforms all other modes. Compatibility ------------- diff --git a/Documentation/filesystems/files.txt b/Documentation/filesystems/files.txt index 133e213ebb7..bb0142f6108 100644 --- a/Documentation/filesystems/files.txt +++ b/Documentation/filesystems/files.txt @@ -76,13 +76,13 @@ the fdtable structure - 5. Handling of the file structures is special. Since the look-up of the fd (fget()/fget_light()) are lock-free, it is possible that look-up may race with the last put() operation on the - file structure. This is avoided using the rcuref APIs + file structure. This is avoided using atomic_inc_not_zero() on ->f_count : rcu_read_lock(); file = fcheck_files(files, fd); if (file) { - if (rcuref_inc_lf(&file->f_count)) + if (atomic_inc_not_zero(&file->f_count)) *fput_needed = 1; else /* Didn't get the reference, someone's freed */ @@ -92,7 +92,7 @@ the fdtable structure - .... return file; - rcuref_inc_lf() detects if refcounts is already zero or + atomic_inc_not_zero() detects if refcounts is already zero or goes to zero during increment. If it does, we fail fget()/fget_light(). diff --git a/Documentation/filesystems/locks.txt b/Documentation/filesystems/locks.txt new file mode 100644 index 00000000000..fab857accbd --- /dev/null +++ b/Documentation/filesystems/locks.txt @@ -0,0 +1,67 @@ + File Locking Release Notes + + Andy Walker <andy@lysaker.kvaerner.no> + + 12 May 1997 + + +1. What's New? +-------------- + +1.1 Broken Flock Emulation +-------------------------- + +The old flock(2) emulation in the kernel was swapped for proper BSD +compatible flock(2) support in the 1.3.x series of kernels. With the +release of the 2.1.x kernel series, support for the old emulation has +been totally removed, so that we don't need to carry this baggage +forever. + +This should not cause problems for anybody, since everybody using a +2.1.x kernel should have updated their C library to a suitable version +anyway (see the file "Documentation/Changes".) + +1.2 Allow Mixed Locks Again +--------------------------- + +1.2.1 Typical Problems - Sendmail +--------------------------------- +Because sendmail was unable to use the old flock() emulation, many sendmail +installations use fcntl() instead of flock(). This is true of Slackware 3.0 +for example. This gave rise to some other subtle problems if sendmail was +configured to rebuild the alias file. Sendmail tried to lock the aliases.dir +file with fcntl() at the same time as the GDBM routines tried to lock this +file with flock(). With pre 1.3.96 kernels this could result in deadlocks that, +over time, or under a very heavy mail load, would eventually cause the kernel +to lock solid with deadlocked processes. + + +1.2.2 The Solution +------------------ +The solution I have chosen, after much experimentation and discussion, +is to make flock() and fcntl() locks oblivious to each other. Both can +exists, and neither will have any effect on the other. + +I wanted the two lock styles to be cooperative, but there were so many +race and deadlock conditions that the current solution was the only +practical one. It puts us in the same position as, for example, SunOS +4.1.x and several other commercial Unices. The only OS's that support +cooperative flock()/fcntl() are those that emulate flock() using +fcntl(), with all the problems that implies. + + +1.3 Mandatory Locking As A Mount Option +--------------------------------------- + +Mandatory locking, as described in 'Documentation/filesystems/mandatory.txt' +was prior to this release a general configuration option that was valid for +all mounted filesystems. This had a number of inherent dangers, not the +least of which was the ability to freeze an NFS server by asking it to read +a file for which a mandatory lock existed. + +From this release of the kernel, mandatory locking can be turned on and off +on a per-filesystem basis, using the mount options 'mand' and 'nomand'. +The default is to disallow mandatory locking. The intention is that +mandatory locking only be enabled on a local filesystem as the specific need +arises. + diff --git a/Documentation/filesystems/mandatory-locking.txt b/Documentation/filesystems/mandatory-locking.txt new file mode 100644 index 00000000000..0979d1d2ca8 --- /dev/null +++ b/Documentation/filesystems/mandatory-locking.txt @@ -0,0 +1,171 @@ + Mandatory File Locking For The Linux Operating System + + Andy Walker <andy@lysaker.kvaerner.no> + + 15 April 1996 + (Updated September 2007) + +0. Why you should avoid mandatory locking +----------------------------------------- + +The Linux implementation is prey to a number of difficult-to-fix race +conditions which in practice make it not dependable: + + - The write system call checks for a mandatory lock only once + at its start. It is therefore possible for a lock request to + be granted after this check but before the data is modified. + A process may then see file data change even while a mandatory + lock was held. + - Similarly, an exclusive lock may be granted on a file after + the kernel has decided to proceed with a read, but before the + read has actually completed, and the reading process may see + the file data in a state which should not have been visible + to it. + - Similar races make the claimed mutual exclusion between lock + and mmap similarly unreliable. + +1. What is mandatory locking? +------------------------------ + +Mandatory locking is kernel enforced file locking, as opposed to the more usual +cooperative file locking used to guarantee sequential access to files among +processes. File locks are applied using the flock() and fcntl() system calls +(and the lockf() library routine which is a wrapper around fcntl().) It is +normally a process' responsibility to check for locks on a file it wishes to +update, before applying its own lock, updating the file and unlocking it again. +The most commonly used example of this (and in the case of sendmail, the most +troublesome) is access to a user's mailbox. The mail user agent and the mail +transfer agent must guard against updating the mailbox at the same time, and +prevent reading the mailbox while it is being updated. + +In a perfect world all processes would use and honour a cooperative, or +"advisory" locking scheme. However, the world isn't perfect, and there's +a lot of poorly written code out there. + +In trying to address this problem, the designers of System V UNIX came up +with a "mandatory" locking scheme, whereby the operating system kernel would +block attempts by a process to write to a file that another process holds a +"read" -or- "shared" lock on, and block attempts to both read and write to a +file that a process holds a "write " -or- "exclusive" lock on. + +The System V mandatory locking scheme was intended to have as little impact as +possible on existing user code. The scheme is based on marking individual files +as candidates for mandatory locking, and using the existing fcntl()/lockf() +interface for applying locks just as if they were normal, advisory locks. + +Note 1: In saying "file" in the paragraphs above I am actually not telling +the whole truth. System V locking is based on fcntl(). The granularity of +fcntl() is such that it allows the locking of byte ranges in files, in addition +to entire files, so the mandatory locking rules also have byte level +granularity. + +Note 2: POSIX.1 does not specify any scheme for mandatory locking, despite +borrowing the fcntl() locking scheme from System V. The mandatory locking +scheme is defined by the System V Interface Definition (SVID) Version 3. + +2. Marking a file for mandatory locking +--------------------------------------- + +A file is marked as a candidate for mandatory locking by setting the group-id +bit in its file mode but removing the group-execute bit. This is an otherwise +meaningless combination, and was chosen by the System V implementors so as not +to break existing user programs. + +Note that the group-id bit is usually automatically cleared by the kernel when +a setgid file is written to. This is a security measure. The kernel has been +modified to recognize the special case of a mandatory lock candidate and to +refrain from clearing this bit. Similarly the kernel has been modified not +to run mandatory lock candidates with setgid privileges. + +3. Available implementations +---------------------------- + +I have considered the implementations of mandatory locking available with +SunOS 4.1.x, Solaris 2.x and HP-UX 9.x. + +Generally I have tried to make the most sense out of the behaviour exhibited +by these three reference systems. There are many anomalies. + +All the reference systems reject all calls to open() for a file on which +another process has outstanding mandatory locks. This is in direct +contravention of SVID 3, which states that only calls to open() with the +O_TRUNC flag set should be rejected. The Linux implementation follows the SVID +definition, which is the "Right Thing", since only calls with O_TRUNC can +modify the contents of the file. + +HP-UX even disallows open() with O_TRUNC for a file with advisory locks, not +just mandatory locks. That would appear to contravene POSIX.1. + +mmap() is another interesting case. All the operating systems mentioned +prevent mandatory locks from being applied to an mmap()'ed file, but HP-UX +also disallows advisory locks for such a file. SVID actually specifies the +paranoid HP-UX behaviour. + +In my opinion only MAP_SHARED mappings should be immune from locking, and then +only from mandatory locks - that is what is currently implemented. + +SunOS is so hopeless that it doesn't even honour the O_NONBLOCK flag for +mandatory locks, so reads and writes to locked files always block when they +should return EAGAIN. + +I'm afraid that this is such an esoteric area that the semantics described +below are just as valid as any others, so long as the main points seem to +agree. + +4. Semantics +------------ + +1. Mandatory locks can only be applied via the fcntl()/lockf() locking + interface - in other words the System V/POSIX interface. BSD style + locks using flock() never result in a mandatory lock. + +2. If a process has locked a region of a file with a mandatory read lock, then + other processes are permitted to read from that region. If any of these + processes attempts to write to the region it will block until the lock is + released, unless the process has opened the file with the O_NONBLOCK + flag in which case the system call will return immediately with the error + status EAGAIN. + +3. If a process has locked a region of a file with a mandatory write lock, all + attempts to read or write to that region block until the lock is released, + unless a process has opened the file with the O_NONBLOCK flag in which case + the system call will return immediately with the error status EAGAIN. + +4. Calls to open() with O_TRUNC, or to creat(), on a existing file that has + any mandatory locks owned by other processes will be rejected with the + error status EAGAIN. + +5. Attempts to apply a mandatory lock to a file that is memory mapped and + shared (via mmap() with MAP_SHARED) will be rejected with the error status + EAGAIN. + +6. Attempts to create a shared memory map of a file (via mmap() with MAP_SHARED) + that has any mandatory locks in effect will be rejected with the error status + EAGAIN. + +5. Which system calls are affected? +----------------------------------- + +Those which modify a file's contents, not just the inode. That gives read(), +write(), readv(), writev(), open(), creat(), mmap(), truncate() and +ftruncate(). truncate() and ftruncate() are considered to be "write" actions +for the purposes of mandatory locking. + +The affected region is usually defined as stretching from the current position +for the total number of bytes read or written. For the truncate calls it is +defined as the bytes of a file removed or added (we must also consider bytes +added, as a lock can specify just "the whole file", rather than a specific +range of bytes.) + +Note 3: I may have overlooked some system calls that need mandatory lock +checking in my eagerness to get this code out the door. Please let me know, or +better still fix the system calls yourself and submit a patch to me or Linus. + +6. Warning! +----------- + +Not even root can override a mandatory lock, so runaway processes can wreak +havoc if they lock crucial files. The way around it is to change the file +permissions (remove the setgid bit) before trying to read or write to it. +Of course, that might be a bit tricky if the system is hung :-( + diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 4a37e25e694..dec99455321 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -347,7 +347,35 @@ connects the CPUs in a SMP system. This means that an error has been detected, the IO-APIC automatically retry the transmission, so it should not be a big problem, but you should read the SMP-FAQ. -In this context it could be interesting to note the new irq directory in 2.4. +In 2.6.2* /proc/interrupts was expanded again. This time the goal was for +/proc/interrupts to display every IRQ vector in use by the system, not +just those considered 'most important'. The new vectors are: + + THR -- interrupt raised when a machine check threshold counter + (typically counting ECC corrected errors of memory or cache) exceeds + a configurable threshold. Only available on some systems. + + TRM -- a thermal event interrupt occurs when a temperature threshold + has been exceeded for the CPU. This interrupt may also be generated + when the temperature drops back to normal. + + SPU -- a spurious interrupt is some interrupt that was raised then lowered + by some IO device before it could be fully processed by the APIC. Hence + the APIC sees the interrupt but does not know what device it came from. + For this case the APIC will generate the interrupt with a IRQ vector + of 0xff. This might also be generated by chipset bugs. + + RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are + sent from one CPU to another per the needs of the OS. Typically, + their statistics are used by kernel developers and interested users to + determine the occurance of interrupt of the given type. + +The above IRQ vectors are displayed only when relevent. For example, +the threshold vector does not exist on x86_64 platforms. Others are +suppressed when the system is a uniprocessor. As of this writing, only +i386 and x86_64 platforms support the new IRQ vector displays. + +Of some interest is the introduction of the /proc/irq directory to 2.4. It could be used to set IRQ to CPU affinity, this means that you can "hook" an IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask @@ -785,9 +813,9 @@ Various pieces of information about kernel activity are available in the since the system first booted. For a quick look, simply cat the file: > cat /proc/stat - cpu 2255 34 2290 22625563 6290 127 456 - cpu0 1132 34 1441 11311718 3675 127 438 - cpu1 1123 0 849 11313845 2614 0 18 + cpu 2255 34 2290 22625563 6290 127 456 0 + cpu0 1132 34 1441 11311718 3675 127 438 0 + cpu1 1123 0 849 11313845 2614 0 18 0 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] ctxt 1990473 btime 1062191376 @@ -807,6 +835,7 @@ second). The meanings of the columns are as follows, from left to right: - iowait: waiting for I/O to complete - irq: servicing interrupts - softirq: servicing softirqs +- steal: involuntary wait The "intr" line gives counts of interrupts serviced since boot time, for each of the possible system interrupts. The first column is the total of all diff --git a/Documentation/filesystems/quota.txt b/Documentation/filesystems/quota.txt new file mode 100644 index 00000000000..a590c4093ef --- /dev/null +++ b/Documentation/filesystems/quota.txt @@ -0,0 +1,59 @@ + +Quota subsystem +=============== + +Quota subsystem allows system administrator to set limits on used space and +number of used inodes (inode is a filesystem structure which is associated +with each file or directory) for users and/or groups. For both used space and +number of used inodes there are actually two limits. The first one is called +softlimit and the second one hardlimit. An user can never exceed a hardlimit +for any resource. User is allowed to exceed softlimit but only for limited +period of time. This period is called "grace period" or "grace time". When +grace time is over, user is not able to allocate more space/inodes until he +frees enough of them to get below softlimit. + +Quota limits (and amount of grace time) are set independently for each +filesystem. + +For more details about quota design, see the documentation in quota-tools package +(http://sourceforge.net/projects/linuxquota). + +Quota netlink interface +======================= +When user exceeds a softlimit, runs out of grace time or reaches hardlimit, +quota subsystem traditionally printed a message to the controlling terminal of +the process which caused the excess. This method has the disadvantage that +when user is using a graphical desktop he usually cannot see the message. +Thus quota netlink interface has been designed to pass information about +the above events to userspace. There they can be captured by an application +and processed accordingly. + +The interface uses generic netlink framework (see +http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more +details about this layer). The name of the quota generic netlink interface +is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>. + Currently, the interface supports only one message type QUOTA_NL_C_WARNING. +This command is used to send a notification about any of the above mentioned +events. Each message has six attributes. These are (type of the argument is +in parentheses): + QUOTA_NL_A_QTYPE (u32) + - type of quota being exceeded (one of USRQUOTA, GRPQUOTA) + QUOTA_NL_A_EXCESS_ID (u64) + - UID/GID (depends on quota type) of user / group whose limit + is being exceeded. + QUOTA_NL_A_CAUSED_ID (u64) + - UID of a user who caused the event + QUOTA_NL_A_WARNING (u32) + - what kind of limit is exceeded: + QUOTA_NL_IHARDWARN - inode hardlimit + QUOTA_NL_ISOFTLONGWARN - inode softlimit is exceeded longer + than given grace period + QUOTA_NL_ISOFTWARN - inode softlimit + QUOTA_NL_BHARDWARN - space (block) hardlimit + QUOTA_NL_BSOFTLONGWARN - space (block) softlimit is exceeded + longer than given grace period. + QUOTA_NL_BSOFTWARN - space (block) softlimit + QUOTA_NL_A_DEV_MAJOR (u32) + - major number of a device with the affected filesystem + QUOTA_NL_A_DEV_MINOR (u32) + - minor number of a device with the affected filesystem diff --git a/Documentation/filesystems/ramfs-rootfs-initramfs.txt b/Documentation/filesystems/ramfs-rootfs-initramfs.txt index 25981e2e51b..339c6a4f220 100644 --- a/Documentation/filesystems/ramfs-rootfs-initramfs.txt +++ b/Documentation/filesystems/ramfs-rootfs-initramfs.txt @@ -8,7 +8,7 @@ What is ramfs? Ramfs is a very simple filesystem that exports Linux's disk caching mechanisms (the page cache and dentry cache) as a dynamically resizable -ram-based filesystem. +RAM-based filesystem. Normally all files are cached in memory by Linux. Pages of data read from backing store (usually the block device the filesystem is mounted on) are kept @@ -34,7 +34,7 @@ ramfs and ramdisk: ------------------ The older "ram disk" mechanism created a synthetic block device out of -an area of ram and used it as backing store for a filesystem. This block +an area of RAM and used it as backing store for a filesystem. This block device was of fixed size, so the filesystem mounted on it was of fixed size. Using a ram disk also required unnecessarily copying memory from the fake block device into the page cache (and copying changes back out), as well @@ -46,8 +46,8 @@ unnecessary work for the CPU, and pollutes the CPU caches. (There are tricks to avoid this copying by playing with the page tables, but they're unpleasantly complicated and turn out to be about as expensive as the copying anyway.) More to the point, all the work ramfs is doing has to happen _anyway_, -since all file access goes through the page and dentry caches. The ram -disk is simply unnecessary, ramfs is internally much simpler. +since all file access goes through the page and dentry caches. The RAM +disk is simply unnecessary; ramfs is internally much simpler. Another reason ramdisks are semi-obsolete is that the introduction of loopback devices offered a more flexible and convenient way to create @@ -103,7 +103,7 @@ All this differs from the old initrd in several ways: initramfs archive is a gzipped cpio archive (like tar only simpler, see cpio(1) and Documentation/early-userspace/buffer-format.txt). The kernel's cpio extraction code is not only extremely small, it's also - __init data that can be discarded during the boot process. + __init text and data that can be discarded during the boot process. - The program run by the old initrd (which was called /initrd, not /init) did some setup and then returned to the kernel, while the init program from @@ -220,7 +220,7 @@ device) but the separate packaging of initrd (which is nice if you have non-GPL code you'd like to run from initramfs, without conflating it with the GPL licensed Linux kernel binary). -It can also be used to supplement the kernel's built-in initamfs image. The +It can also be used to supplement the kernel's built-in initramfs image. The files in the external archive will overwrite any conflicting files in the built-in initramfs archive. Some distributors also prefer to customize a single kernel image with task-specific initramfs images, without recompiling. @@ -339,7 +339,7 @@ smooth transition and allowing early boot functionality to gradually move to The move to early userspace is necessary because finding and mounting the real root device is complex. Root partitions can span multiple devices (raid or separate journal). They can be out on the network (requiring dhcp, setting a -specific mac address, logging into a server, etc). They can live on removable +specific MAC address, logging into a server, etc). They can live on removable media, with dynamically allocated major/minor numbers and persistent naming issues requiring a full udev implementation to sort out. They can be compressed, encrypted, copy-on-write, loopback mounted, strangely partitioned, diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 4b5ca26e504..4598ef7b622 100644 --- a/Documentation/filesystems/sysfs.txt +++ b/Documentation/filesystems/sysfs.txt @@ -51,7 +51,7 @@ for the attributes, providing a means to read and write kernel attributes. Attributes should be ASCII text files, preferably with only one value -per file. It is noted that it may not be efficient to contain only +per file. It is noted that it may not be efficient to contain only one value per file, so it is socially acceptable to express an array of values of the same type. diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 045f3e055a2..9d019d35728 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -537,6 +537,12 @@ struct address_space_operations { struct list_head *pages, unsigned nr_pages); int (*prepare_write)(struct file *, struct page *, unsigned, unsigned); int (*commit_write)(struct file *, struct page *, unsigned, unsigned); + int (*write_begin)(struct file *, struct address_space *mapping, + loff_t pos, unsigned len, unsigned flags, + struct page **pagep, void **fsdata); + int (*write_end)(struct file *, struct address_space *mapping, + loff_t pos, unsigned len, unsigned copied, + struct page *page, void *fsdata); sector_t (*bmap)(struct address_space *, sector_t); int (*invalidatepage) (struct page *, unsigned long); int (*releasepage) (struct page *, int); @@ -615,11 +621,7 @@ struct address_space_operations { any basic-blocks on storage, then those blocks should be pre-read (if they haven't been read already) so that the updated blocks can be written out properly. - The page will be locked. If prepare_write wants to unlock the - page it, like readpage, may do so and return - AOP_TRUNCATED_PAGE. - In this case the prepare_write will be retried one the lock is - regained. + The page will be locked. Note: the page _must not_ be marked uptodate in this function (or anywhere else) unless it actually is uptodate right now. As @@ -633,6 +635,45 @@ struct address_space_operations { operations. It should avoid returning an error if possible - errors should have been handled by prepare_write. + write_begin: This is intended as a replacement for prepare_write. The + key differences being that: + - it returns a locked page (in *pagep) rather than being + given a pre locked page; + - it must be able to cope with short writes (where the + length passed to write_begin is greater than the number + of bytes copied into the page). + + Called by the generic buffered write code to ask the filesystem to + prepare to write len bytes at the given offset in the file. The + address_space should check that the write will be able to complete, + by allocating space if necessary and doing any other internal + housekeeping. If the write will update parts of any basic-blocks on + storage, then those blocks should be pre-read (if they haven't been + read already) so that the updated blocks can be written out properly. + + The filesystem must return the locked pagecache page for the specified + offset, in *pagep, for the caller to write into. + + flags is a field for AOP_FLAG_xxx flags, described in + include/linux/fs.h. + + A void * may be returned in fsdata, which then gets passed into + write_end. + + Returns 0 on success; < 0 on failure (which is the error code), in + which case write_end is not called. + + write_end: After a successful write_begin, and data copy, write_end must + be called. len is the original len passed to write_begin, and copied + is the amount that was able to be copied (copied == len is always true + if write_begin was called with the AOP_FLAG_UNINTERRUPTIBLE flag). + + The filesystem must take care of unlocking the page and releasing it + refcount, and updating i_size. + + Returns < 0 on failure, otherwise the number of bytes (<= 'copied') + that were able to be copied into pagecache. + bmap: called by the VFS to map a logical block offset within object to physical block number. This method is used by the FIBMAP ioctl and for working with swap-files. To be able to swap to @@ -665,7 +706,7 @@ struct address_space_operations { wants to make it a free page. If ->releasepage succeeds, the page will be removed from the address_space and become free. - The second case if when a request has been made to invalidate + The second case is when a request has been made to invalidate some or all pages in an address_space. This can happen through the fadvice(POSIX_FADV_DONTNEED) system call or by the filesystem explicitly requesting it as nfs and 9fs do (when |