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[dragonfly.git] / doc / porting_drivers.txt
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1 PORTING FREEBSD DRIVERS TO DRAGONFLY
2
3* Copy the driver code to the appropriate DragonFly directory. For example,
4 a disk driver /usr/src/sys/dev/blah in FreeBSD would likely be
5 /usr/src/sys/dev/disk/blah in DragonFly.
6
efb850f9 7* Keep all the SVN IDs in the files as a future reference point. dports' SVN
45fa0bf8 8 will do that by default. When using the FreeBSD git repo, please note the
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9 files' IDs manually, either in the files themselves or in the commit message.
10 The general idea is that it must not get lost.
e732300c 11
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12* Driver local #include's probably use a <dev/blah/blah.h> path. These
13 need to be changed to "blah.h". '.' is not included in the #include
14 path in FreeBSD builds, but it is in DragonFly builds.
15
16* Other #include's may reference things in <dev/...> which in DragonFly
17 reside in <bus/...>. In particular, dev/pccard becomes bus/pccard.
18 Note that defines in FreeBSD's pccard_cis.h reside in DragonFly's
19 pccardreg.h .
20
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21* The following kernel functions have been renamed in DragonFly:
22
23 malloc(), free() etc. -> kmalloc(), kfree() etc.
24 printf() etc. -> kprintf() etc.
25 psignal() -> ksignal()
d2da76f2 26 random() -> krandom()
07d0d38c 27
4993a92b 28* MUTEX conversion - mutexes are generally replaced by spinlocks. However,
72e64973 29 DragonFly spinlocks are more restrictive than FreeBSD mutexes so a
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30 direct replacement is not necessarily appropriate in all cases. A lockmgr
31 lock should be used when a direct replacement is not appropriate.
32 In particular, DragonFly does not allow recursive exclusive spinlocks
33 and does not allow multiple exclusive spinlocks to be held by any given
34 thread.
35
36 Instances of <sys/mutex.h> should be replaced with <sys/spinlock.h>.
37
38 When replacing mutexes with spinlocks it is a good idea to rename
39 the structural field (typically 'mtx') to something else (typically 'spin').
40
41 The &Giant mutex is typically converted to get_mplock() and rel_mplock().
42 However, there are places where FreeBSD unlocks giant around some code and
43 then relocks giant... those should simply be removed.
44
45 FreeBSD has weird callout + mutex functions. DragonFly does not integrate
46 the two. Instead, the driver in DragonFly must obtain the spinlocks
47 in question in the callback routine.
48
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49 As a rule of thumb, MTX_DEF mutexes should be replaced with exclusive,
50 recursive lockmgr locks.
51
52 So, suppose the original code is using
53 struct mtx my_mtx;
54 you'd normally rename it to
55 struct lock my_lock;
56
57 and change the initialization from something like
58 mtx_init(&my_mtx, "mymtx", "whatever", MTX_DEF);
59 to
60e7fae5 60 lockinit(&my_lock, "mylock", 0, LK_CANRECURSE);
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61
62 Destroying it is trivial,
63 mtx_destroy(&my_mtx);
64 becomes
65 lockuninit(&my_lock);
66
67 You use the same function for locking and unlocking a lockmgr lock,
68 so exchange
69 mtx_lock(&my_mtx);
70 with
71 lockmgr(&my_lock, LK_EXCLUSIVE);
72 and
73 mtx_unlock(&my_mtx);
74 with
75 lockmgr(&my_lock, LK_RELEASE);
76
77 For testing the lock status, one would use
78 lockstatus(&my_lock, curthread);
79 in place of
80 mtx_owned(&my_mtx);
81
82 An
83 mtx_trylock(&my_mtx);
84 call is replaced with
85 lockmgr(&my_lock, LK_EXCLUSIVE|LK_NOWAIT);
86
87 As for mtx_assert() calls, translate them like this:
88
89 mtx_assert(&my_mtx, MA_OWNED) -> KKASSERT(lockstatus(&my_lock, curthread) != 0)
90 mtx_assert(&my_mtx, MA_NOTOWNED) -> KKASSERT(lockstatus(&my_lock, curthread) == 0)
91
92 In DragonFly, lockstatus() does not return information about whether there have been
93 recursive lock acquisitions, so there is no generic way to emulate the
94
95 mtx_assert(&my_mtx, MA_OWNED|MA_RECURSED);
96 mtx_assert(&my_mtx, MA_OWNED|MA_NOTRECURSED);
97
98 calls.
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99
100* rwlock conversion: Use lockmgr locks
72e64973 101
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102* UMA conversion - generally speaking UMA should be converted to a standard
103 kmalloc.
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104
105 Note however that in FreeBSD M_NOWAIT is often used in cases where, in fact,
07d0d38c 106 the kmalloc cannot fail without blowing something up or causing a fatal
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107 (and very unexpected) I/O error. M_INTWAIT should be used for these cases.
108
109* CDEVSW conversion - see other devices. Generally speaking a major number
110 is needed and a function map needs to be specified more explicitly.
111
112 Most calls passing struct cdev pointers are dev_t's in DragonFly.
113
114 All device vectors in DragonFly pass a dev_<name>_args structure pointer
115 instead of explicit arguments.
116
117 Strategy calls - we pass BIO's and a lot of BUF fields are in the BIO
118 in FreeBSD, but left in the BUF in DragonFly. FreeBSD for some reason
119 names its struct bio pointers 'bp', its a good idea to rename them to 'bio'
120 to avoid confusion and have a struct buf *bp = bio->bio_buf; pointer to
121 access the buf.
122
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123* MSLEEP/TSLEEP conversion. The DragonFly msleep/tsleep do not have 'PRI'
124 priorities. 0 should be used.
4993a92b 125
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126* BUS_* FUNCTIONS
127
128 bus_setup_intr() - replace INTR_TYPE_* flags with 0. There is an extra
129 argument for an interrupt interlock using the sys/serializer.h interface.
60e7fae5 130 This can either be left NULL or you can convert the spinlock(s) for
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131 the driver into serializer locks and integrate the interrupt service
132 routine with a serializer.
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133
134* CAM CODE - cam_simq* code refcounts, so shared device queues (raid and
135 multi-channel devices) are not freed before all references have gone
136 away.
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137
138* callout_drain() should be replaced by callout_stop_sync()
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139
140* UNRHDR functions - DragonFly uses a more generic idr(9) subsystem
141 compatible with the Linux API of the same name
142
143 This LWN article describes it in details: http://lwn.net/Articles/103209/
144
145 A typical conversion looks like this:
146
147 #include <sys/idr.h>
148
149 free_unr() has to be replaced by idr_remove()
150
151 alloc_unr() has to be replaced by a code sequence using idr_pre_get and
152 idr_get_new such as this one:
153
154 retry:
155 if (idr_pre_get(xxx) ==0) {
156 kprintf("Memory allocation error\n");
157 return error;
158 }
159 spin_lock(xxx);
160 ret = idr_get_new(xxx);
161 spin_unlock(xxx);
162 if (ret == EAGAIN)
163 goto retry;
164
4dd401bd 165* MPASS macro - Replace it with KKASSERT
2764c241 166
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167
168* PROC_LOCK / PROC_UNLOCK: to be determined on a case-by-case basis
169
170 Some of the time these macros can be removed entirely
171
172 In some cases, some locking must be done; lwkt_gettoken(&proc_token)
173 and the corresponding lwkt_reltoken() call should be good replacements
174
175 It is not a good idea to blindly implement these macros globally, some
176 particular proc subsystem locking semantics differ enough between FreeBSD
177 and DragonFly that this would cause problems
178
179
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180* In DragonFly 3.3 format specifier %D was removed from kprintf. As a
181 replacement functions kether_ntoa() and hexncpy() were added.
182
183 - Ethernet address (MAC) to its hexadecimal form:
184
185 char ethstr[ETHER_ADDRSTRLEN + 1];
186 u_char hwaddr[6];
187
188 kprintf("MAC address %s\n", kether_ntoa(hwaddr, ethstr)
189
190 - Generic conversion (block of bytes to hexadecimal form):
191
192 char hexstr[18];
193 u_char mydata[6] = {1, 2, 3, 4, 5 ,6};
194
195 /*
196 * Below statement would print:
197 *
198 * 01-02-03-04-05-06
199 */
200 kprintf("%s\n", hexncpy(mydata, 6, hexstr, HEX_NCPYLEN(6), "-"));
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201
202* TAILQ_XXX_SAFE
203
204 Use TAILQ_XXX_MUTABLE; the macros have the same effect, only the name is
205 different
206
207* kern_yield()
208
209 Replace by lwkt_yield()
210
211* vm_page_lock() and vm_page_unlock()
212
213 Not needed on DragonFly, remove these calls
214
215* vm_pager_get_pages()
216
217 Removed, use vm_pager_get_page() instead
218
219* VPO_BUSY
220
221 Replace by PG_BUSY
222
223* kern_psignal()
224
225 Replace by ksignal()