freebsd/lib/libmt/mt.3

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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" Authors: Ken Merry           (Spectra Logic Corporation)
.\" 
.\" $FreeBSD$
.\"
.Dd February 13, 2015
.Dt MT 3
.Os
.Sh NAME
.Nm mt_start_element ,
.Nm mt_end_element ,
.Nm mt_char_handler ,
.Nm mt_status_tree_sbuf ,
.Nm mt_status_tree_print ,
.Nm mt_status_entry_free ,
.Nm mt_status_free ,
.Nm mt_entry_sbuf ,
.Nm mt_param_parent_print ,
.Nm mt_param_entry_print ,
.Nm mt_protect_print ,
.Nm mt_param_list ,
.Nm mt_density_name ,
.Nm mt_density_bp ,
.Nm mt_density_num ,
.Nm mt_get_xml_str ,
.Nm mt_get_status
.Nd Magnetic Tape library
.Sh LIBRARY
.Lb libmt
.Sh SYNOPSIS
.In sys/sbuf.h
.In bsdxml.h
.In mtlib.h
.Ft void
.Fo mt_start_element
.Fa "void *user_data"
.Fa "const char *name"
.Fa "const char **attr"
.Fc
.Ft void
.Fo mt_end_element
.Fa "void *user_data"
.Fa "const char *name"
.Fc
.Ft void
.Fo mt_char_handler
.Fa "void *user_data"
.Fa "const XML_Char *str"
.Fa "int len"
.Fc
.Ft void
.Fo mt_status_tree_sbuf
.Fa "struct sbuf *sb"
.Fa "struct mt_status_entry *entry"
.Fa "int indent"
.Fa "void (*sbuf_func)(struct sbuf *sb, struct mt_status_entry *entry, void *arg)"
.Fa "void *arg"
.Fc
.Ft void
.Fo mt_status_tree_print
.Fa "struct mt_status_entry *entry"
.Fa "int indent"
.Fa "void (*print_func)(struct mt_status_entry *entry, void *arg)"
.Fa "void *arg"
.Fc
.Ft "struct mt_status_entry *"
.Fo mt_entry_find
.Fa "struct mt_status_entry *entry"
.Fa "char *name"
.Fc
.Ft "struct mt_status_entry *"
.Fo mt_status_entry_find
.Fa "struct mt_status_data *status_data"
.Fa "char *name"
.Fc
.Ft void
.Fo mt_status_entry_free
.Fa "struct mt_status_entry *entry)"
.Fc
.Ft void
.Fo mt_status_free
.Fa "struct mt_status_data *status_data"
.Fc
.Ft void
.Fo mt_entry_sbuf
.Fa "struct sbuf *sb"
.Fa "struct mt_status_entry *entry"
.Fa "char *fmt"
.Fc
.Ft void
.Fo mt_param_parent_sbuf
.Fa "struct sbuf *sb"
.Fa "struct mt_status_entry *entry"
.Fa "struct mt_print_params *print_params"
.Fc
.Ft void
.Fo mt_param_parent_print
.Fa "struct mt_status_entry *entry"
.Fa "struct mt_print_params *print_params"
.Fc
.Ft void
.Fo mt_param_entry_sbuf
.Fa "struct sbuf *sb"
.Fa "struct mt_status_entry *entry"
.Fa "void *arg"
.Fc
.Ft void
.Fo mt_param_entry_print
.Fa "struct mt_status_entry *entry"
.Fa "void *arg"
.Fc
.Ft int
.Fo mt_protect_print
.Fa "struct mt_status_data *status_data"
.Fa "int verbose"
.Fc
.Ft int
.Fo mt_param_list
.Fa "struct mt_status_data *status_data"
.Fa "char *param_name"
.Fa "int quiet"
.Fc
.Ft "const char *"
.Fo mt_density_name
.Fa "int density_num"
.Fc
.Ft int
.Fo mt_density_bp
.Fa "int density_num"
.Fa "int bpi"
.Fc
.Ft int
.Fo mt_density_num
.Fa "const char *density_name"
.Fc
.Ft int
.Fo mt_get_status
.Fa "char *xml_str"
.Fa "struct mt_status_data *status_data"
.Fc
.Sh DESCRIPTION
The MT library consists of a number of functions designed to aid in
interacting with the
.Xr sa 4
driver.
The
.Xr sa 4
driver returns some status data as XML-formatted strings, and
the primary purpose of this library is to make it easier for the
software developer to parse those strings and extract the status values.
.Pp
The 
.Fn mt_start_element ,
.Fn mt_end_element ,
and
.Fn mt_char_handler
functions are designed to work with the
.Xr libbsdxml 3
library, which is an XML parsing library.
The user data for the XML parser should be set with
.Fn XML_SetUserData
to a zeroed struct
mt_status_data with the entries list initialized.
The element handlers for the XML parser should be set to
.Fn mt_start_element
and
.Fn mt_end_element
with
.Fn XML_SetElementHandler .
The character data handler should be set to
.Fn mt_char_handler
with the
.Fn XML_SetCharacterDataHandler
function.
The error member of the status_data structure will be set to 0 if parsing
is successful, and non-zero if parsing failed.
In the event of a failure, the error_str member will contain an error
message describing the failure.
These functions will build a tree of tape driver status data that can be
searched and printed using the other functions in this library.
.Pp
.Fn mt_status_tree_sbuf
takes the root node of a tree of
.Xr sa 4
driver status information, and displays it in an
.Xr sbuf 9 .
The
.Ar sb
argument is the destination sbuf.
The
.Ar entry
argument is the root of the tree.
The
.Ar indent
argument is the number of characters to indent the output.
Each recursive call to
.Fn mt_status_tree_sbuf
will have the indent level incremented by 2.
The
.Ar sbuf_func
argument is for a user-supplied alternate printing function.
If it is non-NULL, it will be called instead of the default output printing
code.
The
.Ar arg
argument is an argument for the
.Ar sbuf_func
function.
.Pp
The
.Fn mt_status_tree_print
function is the same as the
.Fn mt_status_tree_sbuf
function, except that the tree is printed to standard out instead of to a
sbuf.
.Pp
The
.Fn mt_entry_find
function returns the first entry in the tree starting at
.Ar entry
that matches
.Ar name .
The supplied node name can be a single level name like "foo", or it can
specify mulitple node names that must be matched, for instance "foo.bar.baz".
In the case of a single level name, it will match any node beneath
.Ar entry
that matches
.Ar name .
In the case of a multi-level name like "foo.bar.baz", it will return the
first entry named "baz" whose immediate parent is "bar" and where the
parent of "bar" is named "foo".
.Pp
The
.Fn mt_status_entry_find
is the same as
.Fn mt_entry_find ,
except that it operates on the top level mt_status_data and all
mt_status_entry nodes below it instead of just an mt_status_entry
structure.
.Pp
The
.Fn mt_status_entry_free
function frees the tree of status data underneath
.Ar entry .
.Pp
The
.Fn mt_status_free
function frees the tree of status data underneath
.Ar status_data .
.Pp
The
.Fn mt_entry_sbuf
function prints
.Ar entry
to the supplied sbuf
.Ar sb ,
optionally using the
.Xr printf 3
format
.Ar fmt .
If
.Ar fmt
is NULL, then
.Fn mt_entry_sbuf
will render integer types in base 10 without special formatting and all
other types as they were rendered in the XML.
.Pp
.Fn mt_param_parent_sbuf
prints the parents of the given
.Ar entry
to the supplied sbuf
.Ar sb
subject to the print parameters
.Ar print_params .
The result will be formatted with a period between each level, like
"foo.bar.baz".
.Pp
.Fn mt_param_parent_print
is like
.Fn mt_param_parent_sbuf
except that it prints the results to standard output instead of an sbuf.
.Pp
.Fn mt_param_entry_sbuf
prints the
.Ar entry 
to the given sbuf
.Ar sb .
The argument
.Ar arg
is a pointer to struct mt_print_params, which allows the caller to control
the printing output.
This function is intended to be supplied as an argument to
.Fn mt_status_tree_sbuf .
.Pp
.Fn mt_param_entry_print
is like
.Fn mt_param_entry_sbuf
except that it prints to standard output instead of an sbuf.
It is intended to be used as an argument to
.Fn mt_status_tree_print .
.Pp
.Fn mt_protect_print
prints tape drive protection information from the supplied
.Ar status_data
beginning at the node name defined as the root node for protection data.
If the
.Ar verbose
argument is non-zero, protection entry descriptions will be printed.
If it is zero, protection entry descriptions will not be printed.
.Pp
.Fn mt_param_list
prints tape driver parameters information from the supplied
.Ar status_data .
If the
.Ar param_name
is non-NULL, only the named parameter will be printed.
If
.Ar quiet
is non-zero, parameter descriptions will be omitted in the output.
.Pp
.Fn mt_density_name
Returns a text identifier for the supplied numeric
.Ar density_num .
The
.Ar density_num
should currently be a value between 0 and 255 inclusive, since that is the
valid range for
.Tn SCSI
density code values.
See below for notes on the return values.
.Pp
.Fn mt_density_bp
Returns the bits per inch or bits per mm values for a given density entry
specified by the
.Ar density_num .
If the 
.Ar bpi
argument is non-zero, the bits per inch value is returned.
Otherwise, the bits per mm value is returned.
.Pp
.Fn mt_density_num
returns a numeric value for a text density description.
It does a case-insensitive comparison of density names in the density table
to the supplied density name.
.Pp
.Fn mt_get_xml_str
gets the current XML status / parameter string from the sa(4) driver
instance referenced by the open file descriptor
.Ar mtfd .
The 
.Xr mtio 4 
.Xr ioctl 2
to be used is supplied as the
.Ar cmd
argument.
Currently the
.Fn mt_get_xml_str
function will work with the
.Dv MTIOCEXTGET
and
.Dv MTIOCPARAMGET
ioctls.
The supplied
.Ar xml_str
will be filled in with a pointer to the complete XML status string.
Multiple calls to the given
.Xr ioctl 2
are made and more space is malloced until all of the XML string is fetched.
The string returned in the
.Ar xml_str
argument should be freed when it is no longer in use.
.Sh RETURN VALUES
.Fn mt_entry_find
returns the first matching entry, or NULL if it fails to find a match.
.Pp
.Fn mt_status_entry_find
returns the first matching entry, or NULL if it fails to find a match.
.Pp
.Fn mt_protect_print
Returns 0 for success, and non-zero for failure.
.Fn mt_protect_print
can only fail if it cannot find protection information in the supplied
status data.
.Pp
.Fn mt_param_list
Returns 0 for success and non-zero for failure.
.Fn mt_param_list
can only fail if it cannot find parameter information in the supplied
status data.
.Pp
.Fn mt_density_name
returns a text description of a numeric density.
The special density value 0 is decoded as "default".
The special density value 0x7f is decoded as "same".
If the density is not known,
.Fn mt_density_name
will return "UNKNOWN".
.Pp
.Fn mt_density_bp
returns the bits per inch value for the given density (if the 
.Ar bpi
field is non-zero), the bits per mm value otherwise, or 0 if the supplied
.Ar density_num
is not in the density table or the table entry does not include bpi / bpmm
values.
.Pp
.Fn mt_density_num
returns a numeric density value between 0 and 255 for the supplied density
name.
It returns 0 if the density name is not recognized.
.Pp
.Fn mt_get_xml_str
returns 0 for success, and -1 for failure.
.Sh SEE ALSO
.Xr mt 1 ,
.Xr mtio 4 ,
.Xr sa 4
.Sh HISTORY
The MT library first appeared in
.Fx 10.1 .
.Sh AUTHORS
.An Ken Merry Aq ken@FreeBSD.org
.Sh BUGS
The library interface is not complete, and may change in the future.
Application authors should not rely on the library interface to be
consistent in the immediate future.