file-systems: Remove 'title' field and add <file-system-label>.

The 'title' field was easily overlooked and was an endless source of
confusion.  Now, the value of the 'device' field is self-contained.

* gnu/system/file-systems.scm (<file-system>): Change constructor name
to '%file-system'.
[title]: Remove.
(<file-system-label>): New record type with printer.
(report-deprecation, device-expression)
(process-file-system-declaration, file-system): New macros.
(file-system-title): New procedure.
(file-system->spec, spec->file-system): Adjust to handle
<file-system-label>.
* gnu/system.scm (bootable-kernel-arguments): Add case for
'file-system-label?'.
(read-boot-parameters): Likewise.
(mapped-device-user): Avoid 'file-system-title'.
(fs->boot-device): Remove.
(operating-system-boot-parameters): Use 'file-system-device' instead of
'fs->boot-device'.
(device->sexp): Add case for 'file-system-label?'.
* gnu/bootloader/grub.scm (grub-root-search): Add case for
'file-system-label?'.
* gnu/system/examples/bare-bones.tmpl,
gnu/system/examples/beaglebone-black.tmpl,
gnu/system/examples/lightweight-desktop.tmpl,
gnu/system/examples/vm-image.tmpl: Remove uses of 'title'.
* gnu/system/vm.scm (virtualized-operating-system): Remove uses of
'file-system-title'.
* guix/scripts/system.scm (check-file-system-availability): Likewise,
and adjust fix-it hint.
(check-initrd-modules)[file-system-/dev]: Likewise.
* gnu/build/file-systems.scm (canonicalize-device-spec): Remove 'title'
parameter.
[canonical-title]: Remove.
Match on SPEC's type rather than on CANONICAL-TITLE.
(mount-file-system): Adjust caller.
* gnu/build/linux-boot.scm (boot-system): Interpret ROOT here.
* gnu/services/base.scm (file-system->fstab-entry): Remove use of
'file-system-title'.
* doc/guix.texi (File Systems): Remove documentation of the 'title'
field.  Rewrite documentation of 'device' and document
'file-system-label'.

1 files changed, 25 insertions, 23 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 5129b998bd..5eee40fc3c 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -9210,20 +9210,31 @@ This is a string specifying the type of the file system---e.g.,
 This designates the place where the file system is to be mounted.
 
 @item @code{device}
-This names the ``source'' of the file system.  By default it is the name
-of a node under @file{/dev}, but its meaning depends on the @code{title}
-field described below.
+This names the ``source'' of the file system.  It can be one of three
+things: a file system label, a file system UUID, or the name of a
+@file{/dev} node.  Labels and UUIDs offer a way to refer to file
+systems without having to hard-code their actual device
+name@footnote{Note that, while it is tempting to use
+@file{/dev/disk/by-uuid} and similar device names to achieve the same
+result, this is not recommended: These special device nodes are created
+by the udev daemon and may be unavailable at the time the device is
+mounted.}.
 
-@item @code{title} (default: @code{'device})
-This is a symbol that specifies how the @code{device} field is to be
-interpreted.
+@findex file-system-label
+File system labels are created using the @code{file-system-label}
+procedure, UUIDs are created using @code{uuid}, and @file{/dev} node are
+plain strings.  Here's an example of a file system referred to by its
+label, as shown by the @command{e2label} command:
 
-When it is the symbol @code{device}, then the @code{device} field is
-interpreted as a file name; when it is @code{label}, then @code{device}
-is interpreted as a file system label name; when it is @code{uuid},
-@code{device} is interpreted as a file system unique identifier (UUID).
+@example
+(file-system
+  (mount-point "/home")
+  (type "ext4")
+  (device (file-system-label "my-home")))
+@end example
 
-UUIDs may be converted from their string representation (as shown by the
+@findex uuid
+UUIDs are converted from their string representation (as shown by the
 @command{tune2fs -l} command) using the @code{uuid} form@footnote{The
 @code{uuid} form expects 16-byte UUIDs as defined in
 @uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the
@@ -9235,22 +9246,13 @@ like this:
 (file-system
   (mount-point "/home")
   (type "ext4")
-  (title 'uuid)
   (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
 @end example
 
-The @code{label} and @code{uuid} options offer a way to refer to file
-systems without having to hard-code their actual device
-name@footnote{Note that, while it is tempting to use
-@file{/dev/disk/by-uuid} and similar device names to achieve the same
-result, this is not recommended: These special device nodes are created
-by the udev daemon and may be unavailable at the time the device is
-mounted.}.
-
-However, when the source of a file system is a mapped device (@pxref{Mapped
+When the source of a file system is a mapped device (@pxref{Mapped
 Devices}), its @code{device} field @emph{must} refer to the mapped
-device name---e.g., @file{/dev/mapper/root-partition}---and consequently
-@code{title} must be set to @code{'device}.  This is required so that
+device name---e.g., @file{"/dev/mapper/root-partition"}.
+This is required so that
 the system knows that mounting the file system depends on having the
 corresponding device mapping established.