nilfs2: add comments for ioctls

Add comments for ioctls in fs/nilfs2/ioctl.c file and describe NILFS2
specific ioctls in Documentation/filesystems/nilfs2.txt.
Signed-off-by: NVyacheslav Dubeyko <slava@dubeyko.com>
Reviewed-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Wenliang Fan <fanwlexca@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/nilfs2.txt

@@ -81,6 +81,62 @@ nodiscard(*)		The discard/TRIM commands are sent to the underlying
 			block device when blocks are freed.  This is useful
 			for SSD devices and sparse/thinly-provisioned LUNs.
 
+Ioctls
+======
+
+There is some NILFS2 specific functionality which can be accessed by applications
+through the system call interfaces. The list of all NILFS2 specific ioctls are
+shown in the table below.
+
+Table of NILFS2 specific ioctls
+..............................................................................
+ Ioctl			        Description
+ NILFS_IOCTL_CHANGE_CPMODE      Change mode of given checkpoint between
+			        checkpoint and snapshot state. This ioctl is
+			        used in chcp and mkcp utilities.
+
+ NILFS_IOCTL_DELETE_CHECKPOINT  Remove checkpoint from NILFS2 file system.
+			        This ioctl is used in rmcp utility.
+
+ NILFS_IOCTL_GET_CPINFO         Return info about requested checkpoints. This
+			        ioctl is used in lscp utility and by
+			        nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_GET_CPSTAT         Return checkpoints statistics. This ioctl is
+			        used by lscp, rmcp utilities and by
+			        nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_GET_SUINFO         Return segment usage info about requested
+			        segments. This ioctl is used in lssu,
+			        nilfs_resize utilities and by nilfs_cleanerd
+			        daemon.
+
+ NILFS_IOCTL_GET_SUSTAT         Return segment usage statistics. This ioctl
+			        is used in lssu, nilfs_resize utilities and
+			        by nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_GET_VINFO          Return information on virtual block addresses.
+			        This ioctl is used by nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_GET_BDESCS         Return information about descriptors of disk
+			        block numbers. This ioctl is used by
+			        nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_CLEAN_SEGMENTS     Do garbage collection operation in the
+			        environment of requested parameters from
+			        userspace. This ioctl is used by
+			        nilfs_cleanerd daemon.
+
+ NILFS_IOCTL_SYNC               Make a checkpoint. This ioctl is used in
+			        mkcp utility.
+
+ NILFS_IOCTL_RESIZE             Resize NILFS2 volume. This ioctl is used
+			        by nilfs_resize utility.
+
+ NILFS_IOCTL_SET_ALLOC_RANGE    Define lower limit of segments in bytes and
+			        upper limit of segments in bytes. This ioctl
+			        is used by nilfs_resize utility.
+
 NILFS2 usage
 ============
 

fs/nilfs2/ioctl.c

@@ -37,7 +37,26 @@
 #include "sufile.h"
 #include "dat.h"
 
-
+/**
+ * nilfs_ioctl_wrap_copy - wrapping function of get/set metadata info
+ * @nilfs: nilfs object
+ * @argv: vector of arguments from userspace
+ * @dir: set of direction flags
+ * @dofunc: concrete function of get/set metadata info
+ *
+ * Description: nilfs_ioctl_wrap_copy() gets/sets metadata info by means of
+ * calling dofunc() function on the basis of @argv argument.
+ *
+ * Return Value: On success, 0 is returned and requested metadata info
+ * is copied into userspace. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EINVAL - Invalid arguments from userspace.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EFAULT - Failure during execution of requested operation.
+ */
 static int nilfs_ioctl_wrap_copy(struct the_nilfs *nilfs,
 				 struct nilfs_argv *argv, int dir,
 				 ssize_t (*dofunc)(struct the_nilfs *,
@@ -107,6 +126,9 @@ static int nilfs_ioctl_wrap_copy(struct the_nilfs *nilfs,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_getflags - ioctl to support lsattr
+ */
 static int nilfs_ioctl_getflags(struct inode *inode, void __user *argp)
 {
 	unsigned int flags = NILFS_I(inode)->i_flags & FS_FL_USER_VISIBLE;
@@ -114,6 +136,9 @@ static int nilfs_ioctl_getflags(struct inode *inode, void __user *argp)
 	return put_user(flags, (int __user *)argp);
 }
 
+/**
+ * nilfs_ioctl_setflags - ioctl to support chattr
+ */
 static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 				void __user *argp)
 {
@@ -166,11 +191,33 @@ static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_getversion - get info about a file's version (generation number)
+ */
 static int nilfs_ioctl_getversion(struct inode *inode, void __user *argp)
 {
 	return put_user(inode->i_generation, (int __user *)argp);
 }
 
+/**
+ * nilfs_ioctl_change_cpmode - change checkpoint mode (checkpoint/snapshot)
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_change_cpmode() function changes mode of
+ * given checkpoint between checkpoint and snapshot state. This ioctl
+ * is used in chcp and mkcp utilities.
+ *
+ * Return Value: On success, 0 is returned and mode of a checkpoint is
+ * changed. On error, one of the following negative error codes
+ * is returned.
+ *
+ * %-EPERM - Operation not permitted.
+ *
+ * %-EFAULT - Failure during checkpoint mode changing.
+ */
 static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
 				     unsigned int cmd, void __user *argp)
 {
@@ -206,6 +253,25 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_delete_checkpoint - remove checkpoint
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_delete_checkpoint() function removes
+ * checkpoint from NILFS2 file system. This ioctl is used in rmcp
+ * utility.
+ *
+ * Return Value: On success, 0 is returned and a checkpoint is
+ * removed. On error, one of the following negative error codes
+ * is returned.
+ *
+ * %-EPERM - Operation not permitted.
+ *
+ * %-EFAULT - Failure during checkpoint removing.
+ */
 static int
 nilfs_ioctl_delete_checkpoint(struct inode *inode, struct file *filp,
 			      unsigned int cmd, void __user *argp)
@@ -237,6 +303,21 @@ nilfs_ioctl_delete_checkpoint(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_do_get_cpinfo - callback method getting info about checkpoints
+ * @nilfs: nilfs object
+ * @posp: pointer on array of checkpoint's numbers
+ * @flags: checkpoint mode (checkpoint or snapshot)
+ * @buf: buffer for storing checkponts' info
+ * @size: size in bytes of one checkpoint info item in array
+ * @nmembs: number of checkpoints in array (numbers and infos)
+ *
+ * Description: nilfs_ioctl_do_get_cpinfo() function returns info about
+ * requested checkpoints. The NILFS_IOCTL_GET_CPINFO ioctl is used in
+ * lscp utility and by nilfs_cleanerd daemon.
+ *
+ * Return value: count of nilfs_cpinfo structures in output buffer.
+ */
 static ssize_t
 nilfs_ioctl_do_get_cpinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 			  void *buf, size_t size, size_t nmembs)
@@ -250,6 +331,27 @@ nilfs_ioctl_do_get_cpinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_get_cpstat - get checkpoints statistics
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_get_cpstat() returns information about checkpoints.
+ * The NILFS_IOCTL_GET_CPSTAT ioctl is used by lscp, rmcp utilities
+ * and by nilfs_cleanerd daemon.
+ *
+ * Return Value: On success, 0 is returned, and checkpoints information is
+ * copied into userspace pointer @argp. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EFAULT - Failure during getting checkpoints statistics.
+ */
 static int nilfs_ioctl_get_cpstat(struct inode *inode, struct file *filp,
 				  unsigned int cmd, void __user *argp)
 {
@@ -268,6 +370,21 @@ static int nilfs_ioctl_get_cpstat(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_do_get_suinfo - callback method getting segment usage info
+ * @nilfs: nilfs object
+ * @posp: pointer on array of segment numbers
+ * @flags: *not used*
+ * @buf: buffer for storing suinfo array
+ * @size: size in bytes of one suinfo item in array
+ * @nmembs: count of segment numbers and suinfos in array
+ *
+ * Description: nilfs_ioctl_do_get_suinfo() function returns segment usage
+ * info about requested segments. The NILFS_IOCTL_GET_SUINFO ioctl is used
+ * in lssu, nilfs_resize utilities and by nilfs_cleanerd daemon.
+ *
+ * Return value: count of nilfs_suinfo structures in output buffer.
+ */
 static ssize_t
 nilfs_ioctl_do_get_suinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 			  void *buf, size_t size, size_t nmembs)
@@ -281,6 +398,27 @@ nilfs_ioctl_do_get_suinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_get_sustat - get segment usage statistics
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_get_sustat() returns segment usage statistics.
+ * The NILFS_IOCTL_GET_SUSTAT ioctl is used in lssu, nilfs_resize utilities
+ * and by nilfs_cleanerd daemon.
+ *
+ * Return Value: On success, 0 is returned, and segment usage information is
+ * copied into userspace pointer @argp. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EFAULT - Failure during getting segment usage statistics.
+ */
 static int nilfs_ioctl_get_sustat(struct inode *inode, struct file *filp,
 				  unsigned int cmd, void __user *argp)
 {
@@ -299,6 +437,21 @@ static int nilfs_ioctl_get_sustat(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_do_get_vinfo - callback method getting virtual blocks info
+ * @nilfs: nilfs object
+ * @posp: *not used*
+ * @flags: *not used*
+ * @buf: buffer for storing array of nilfs_vinfo structures
+ * @size: size in bytes of one vinfo item in array
+ * @nmembs: count of vinfos in array
+ *
+ * Description: nilfs_ioctl_do_get_vinfo() function returns information
+ * on virtual block addresses. The NILFS_IOCTL_GET_VINFO ioctl is used
+ * by nilfs_cleanerd daemon.
+ *
+ * Return value: count of nilfs_vinfo structures in output buffer.
+ */
 static ssize_t
 nilfs_ioctl_do_get_vinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 			 void *buf, size_t size, size_t nmembs)
@@ -311,6 +464,21 @@ nilfs_ioctl_do_get_vinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_do_get_bdescs - callback method getting disk block descriptors
+ * @nilfs: nilfs object
+ * @posp: *not used*
+ * @flags: *not used*
+ * @buf: buffer for storing array of nilfs_bdesc structures
+ * @size: size in bytes of one bdesc item in array
+ * @nmembs: count of bdescs in array
+ *
+ * Description: nilfs_ioctl_do_get_bdescs() function returns information
+ * about descriptors of disk block numbers. The NILFS_IOCTL_GET_BDESCS ioctl
+ * is used by nilfs_cleanerd daemon.
+ *
+ * Return value: count of nilfs_bdescs structures in output buffer.
+ */
 static ssize_t
 nilfs_ioctl_do_get_bdescs(struct the_nilfs *nilfs, __u64 *posp, int flags,
 			  void *buf, size_t size, size_t nmembs)
@@ -337,6 +505,29 @@ nilfs_ioctl_do_get_bdescs(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	return nmembs;
 }
 
+/**
+ * nilfs_ioctl_get_bdescs - get disk block descriptors
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_do_get_bdescs() function returns information
+ * about descriptors of disk block numbers. The NILFS_IOCTL_GET_BDESCS ioctl
+ * is used by nilfs_cleanerd daemon.
+ *
+ * Return Value: On success, 0 is returned, and disk block descriptors are
+ * copied into userspace pointer @argp. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EINVAL - Invalid arguments from userspace.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EFAULT - Failure during getting disk block descriptors.
+ */
 static int nilfs_ioctl_get_bdescs(struct inode *inode, struct file *filp,
 				  unsigned int cmd, void __user *argp)
 {
@@ -360,6 +551,26 @@ static int nilfs_ioctl_get_bdescs(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_move_inode_block - prepare data/node block for moving by GC
+ * @inode: inode object
+ * @vdesc: descriptor of virtual block number
+ * @buffers: list of moving buffers
+ *
+ * Description: nilfs_ioctl_move_inode_block() function registers data/node
+ * buffer in the GC pagecache and submit read request.
+ *
+ * Return Value: On success, 0 is returned. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-ENOENT - Requested block doesn't exist.
+ *
+ * %-EEXIST - Blocks conflict is detected.
+ */
 static int nilfs_ioctl_move_inode_block(struct inode *inode,
 					struct nilfs_vdesc *vdesc,
 					struct list_head *buffers)
@@ -405,6 +616,19 @@ static int nilfs_ioctl_move_inode_block(struct inode *inode,
 	return 0;
 }
 
+/**
+ * nilfs_ioctl_move_blocks - move valid inode's blocks during garbage collection
+ * @sb: superblock object
+ * @argv: vector of arguments from userspace
+ * @buf: array of nilfs_vdesc structures
+ *
+ * Description: nilfs_ioctl_move_blocks() function reads valid data/node
+ * blocks that garbage collector specified with the array of nilfs_vdesc
+ * structures and stores them into page caches of GC inodes.
+ *
+ * Return Value: Number of processed nilfs_vdesc structures or
+ * error code, otherwise.
+ */
 static int nilfs_ioctl_move_blocks(struct super_block *sb,
 				   struct nilfs_argv *argv, void *buf)
 {
@@ -470,6 +694,25 @@ static int nilfs_ioctl_move_blocks(struct super_block *sb,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_delete_checkpoints - delete checkpoints
+ * @nilfs: nilfs object
+ * @argv: vector of arguments from userspace
+ * @buf: array of periods of checkpoints numbers
+ *
+ * Description: nilfs_ioctl_delete_checkpoints() function deletes checkpoints
+ * in the period from p_start to p_end, excluding p_end itself. The checkpoints
+ * which have been already deleted are ignored.
+ *
+ * Return Value: Number of processed nilfs_period structures or
+ * error code, otherwise.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EINVAL - invalid checkpoints.
+ */
 static int nilfs_ioctl_delete_checkpoints(struct the_nilfs *nilfs,
 					  struct nilfs_argv *argv, void *buf)
 {
@@ -487,6 +730,24 @@ static int nilfs_ioctl_delete_checkpoints(struct the_nilfs *nilfs,
 	return nmembs;
 }
 
+/**
+ * nilfs_ioctl_free_vblocknrs - free virtual block numbers
+ * @nilfs: nilfs object
+ * @argv: vector of arguments from userspace
+ * @buf: array of virtual block numbers
+ *
+ * Description: nilfs_ioctl_free_vblocknrs() function frees
+ * the virtual block numbers specified by @buf and @argv->v_nmembs.
+ *
+ * Return Value: Number of processed virtual block numbers or
+ * error code, otherwise.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-ENOENT - The virtual block number have not been allocated.
+ */
 static int nilfs_ioctl_free_vblocknrs(struct the_nilfs *nilfs,
 				      struct nilfs_argv *argv, void *buf)
 {
@@ -498,6 +759,24 @@ static int nilfs_ioctl_free_vblocknrs(struct the_nilfs *nilfs,
 	return (ret < 0) ? ret : nmembs;
 }
 
+/**
+ * nilfs_ioctl_mark_blocks_dirty - mark blocks dirty
+ * @nilfs: nilfs object
+ * @argv: vector of arguments from userspace
+ * @buf: array of block descriptors
+ *
+ * Description: nilfs_ioctl_mark_blocks_dirty() function marks
+ * metadata file or data blocks as dirty.
+ *
+ * Return Value: Number of processed block descriptors or
+ * error code, otherwise.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ *
+ * %-EIO - I/O error
+ *
+ * %-ENOENT - the specified block does not exist (hole block)
+ */
 static int nilfs_ioctl_mark_blocks_dirty(struct the_nilfs *nilfs,
 					 struct nilfs_argv *argv, void *buf)
 {
@@ -579,6 +858,20 @@ int nilfs_ioctl_prepare_clean_segments(struct the_nilfs *nilfs,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_clean_segments - clean segments
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_clean_segments() function makes garbage
+ * collection operation in the environment of requested parameters
+ * from userspace. The NILFS_IOCTL_CLEAN_SEGMENTS ioctl is used by
+ * nilfs_cleanerd daemon.
+ *
+ * Return Value: On success, 0 is returned or error code, otherwise.
+ */
 static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
 				      unsigned int cmd, void __user *argp)
 {
@@ -690,6 +983,33 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_sync - make a checkpoint
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ *
+ * Description: nilfs_ioctl_sync() function constructs a logical segment
+ * for checkpointing.  This function guarantees that all modified data
+ * and metadata are written out to the device when it successfully
+ * returned.
+ *
+ * Return Value: On success, 0 is retured. On errors, one of the following
+ * negative error code is returned.
+ *
+ * %-EROFS - Read only filesystem.
+ *
+ * %-EIO - I/O error
+ *
+ * %-ENOSPC - No space left on device (only in a panic state).
+ *
+ * %-ERESTARTSYS - Interrupted.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ *
+ * %-EFAULT - Failure during execution of requested operation.
+ */
 static int nilfs_ioctl_sync(struct inode *inode, struct file *filp,
 			    unsigned int cmd, void __user *argp)
 {
@@ -718,6 +1038,14 @@ static int nilfs_ioctl_sync(struct inode *inode, struct file *filp,
 	return 0;
 }
 
+/**
+ * nilfs_ioctl_resize - resize NILFS2 volume
+ * @inode: inode object
+ * @filp: file object
+ * @argp: pointer on argument from userspace
+ *
+ * Return Value: On success, 0 is returned or error code, otherwise.
+ */
 static int nilfs_ioctl_resize(struct inode *inode, struct file *filp,
 			      void __user *argp)
 {
@@ -743,6 +1071,17 @@ static int nilfs_ioctl_resize(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_set_alloc_range - limit range of segments to be allocated
+ * @inode: inode object
+ * @argp: pointer on argument from userspace
+ *
+ * Decription: nilfs_ioctl_set_alloc_range() function defines lower limit
+ * of segments in bytes and upper limit of segments in bytes.
+ * The NILFS_IOCTL_SET_ALLOC_RANGE is used by nilfs_resize utility.
+ *
+ * Return Value: On success, 0 is returned or error code, otherwise.
+ */
 static int nilfs_ioctl_set_alloc_range(struct inode *inode, void __user *argp)
 {
 	struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
@@ -775,6 +1114,28 @@ static int nilfs_ioctl_set_alloc_range(struct inode *inode, void __user *argp)
 	return ret;
 }
 
+/**
+ * nilfs_ioctl_get_info - wrapping function of get metadata info
+ * @inode: inode object
+ * @filp: file object
+ * @cmd: ioctl's request code
+ * @argp: pointer on argument from userspace
+ * @membsz: size of an item in bytes
+ * @dofunc: concrete function of getting metadata info
+ *
+ * Description: nilfs_ioctl_get_info() gets metadata info by means of
+ * calling dofunc() function.
+ *
+ * Return Value: On success, 0 is returned and requested metadata info
+ * is copied into userspace. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-EINVAL - Invalid arguments from userspace.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EFAULT - Failure during execution of requested operation.
+ */
 static int nilfs_ioctl_get_info(struct inode *inode, struct file *filp,
 				unsigned int cmd, void __user *argp,
 				size_t membsz,