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author | Arnd Bergmann <arnd@arndb.de> | 2018-04-24 20:06:15 +0800 |
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committer | Arnd Bergmann <arnd@arndb.de> | 2019-12-13 11:25:58 +0100 |
commit | 80fe7430c7085951d1246d83f638cc17e6c0be36 (patch) | |
tree | 337c0b0534352e3653880dc072f82842e2290079 /sound/core/pcm_native.c | |
parent | 09d94175dbeac12d38b1599a02c7000a5e51b4cb (diff) | |
download | linux-80fe7430c7085951d1246d83f638cc17e6c0be36.tar.bz2 |
ALSA: add new 32-bit layout for snd_pcm_mmap_status/control
The snd_pcm_mmap_status and snd_pcm_mmap_control interfaces are one of the
trickiest areas to get right when moving to 64-bit time_t in user space.
The snd_pcm_mmap_status structure layout is incompatible with user space
that uses a 64-bit time_t, so we need a new layout for it. Since the
SNDRV_PCM_IOCTL_SYNC_PTR ioctl combines it with snd_pcm_mmap_control
into snd_pcm_sync_ptr, we need to change those two as well.
Both structures are also exported via an mmap() operation on certain
architectures, and this suffers from incompatibility between 32-bit
and 64-bit user space. As we have to change both structures anyway,
this is a good opportunity to fix the mmap() problem as well, so let's
standardize on the existing 64-bit layout of the structure where possible.
The downside is that we lose mmap() support for existing 32-bit x86 and
powerpc applications, adding that would introduce very noticeable runtime
overhead and complexity. My assumption here is that not too many people
will miss the removed feature, given that:
- Almost all x86 and powerpc users these days are on 64-bit kernels,
the majority of today's 32-bit users are on architectures that never
supported mmap (ARM, MIPS, ...).
- It never worked in compat mode (it was intentionally disabled there)
- The application already needs to work with a fallback to
SNDRV_PCM_IOCTL_SYNC_PTR, which will keep working with both the old
and new structure layout.
Both the ioctl() and mmap() based interfaces are changed at the same
time, as they are based on the same structures. Unlike other interfaces,
we change the uapi header to export both the traditional structure and
a version that is portable between 32-bit and 64-bit user space code
and that corresponds to the existing 64-bit layout. We further check the
__USE_TIME_BITS64 macro that will be defined by future C library versions
whenever we use the new time_t definition, so any existing user space
source code will not see any changes until it gets rebuilt against a new
C library. However, the new structures are all visible in addition to the
old ones, allowing applications to explicitly request the new structures.
In order to detect the difference between the old snd_pcm_mmap_status and
the new __snd_pcm_mmap_status64 structure from the ioctl command number,
we rely on one quirk in the structure definition: snd_pcm_mmap_status
must be aligned to alignof(time_t), which leads the compiler to insert
four bytes of padding in struct snd_pcm_sync_ptr after 'flags' and a
corresponding change in the size of snd_pcm_sync_ptr itself. On x86-32
(and only there), the compiler doesn't use 64-bit alignment in structure,
so I'm adding an explicit pad in the structure that has no effect on the
existing 64-bit architectures but ensures that the layout matches for x86.
The snd_pcm_uframes_t type compatibility requires another hack: we can't
easily make that 64 bit wide, so I leave the type as 'unsigned long',
but add padding before and after it, to ensure that the data is properly
aligned to the respective 64-bit field in the in-kernel structure.
For the SNDRV_PCM_MMAP_OFFSET_STATUS/CONTROL constants that are used
as the virtual file offset in the mmap() function, we also have to
introduce new constants that depend on hte __USE_TIME_BITS64 macro:
The existing macros are renamed to SNDRV_PCM_MMAP_OFFSET_STATUS_OLD
and SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD, they continue to work fine on
64-bit architectures, but stop working on native 32-bit user space.
The replacement _NEW constants are now used by default for user space
built with __USE_TIME_BITS64, those now work on all new kernels for x86,
ppc and alpha (32 and 64 bit, native and compat). It might be a good idea
for a future alsa-lib to support both the _OLD and _NEW macros and use
the corresponding structures directly. Unmodified alsa-lib source code
will retain the current behavior, so it will no longer be able to use
mmap() for the status/control structures on 32-bit systems, until either
the C library gets updated to 64-bit time_t or alsa-lib gets updated to
support both mmap() layouts.
Co-developed-with: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'sound/core/pcm_native.c')
-rw-r--r-- | sound/core/pcm_native.c | 38 |
1 files changed, 24 insertions, 14 deletions
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index ba0636a2b437..5a1245509eac 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2889,14 +2889,15 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream, return 0; } -#ifdef CONFIG_COMPAT struct snd_pcm_mmap_status32 { s32 state; s32 pad1; u32 hw_ptr; - struct compat_timespec tstamp; + s32 tstamp_sec; + s32 tstamp_nsec; s32 suspended_state; - struct compat_timespec audio_tstamp; + s32 audio_tstamp_sec; + s32 audio_tstamp_nsec; } __attribute__((packed)); struct snd_pcm_mmap_control32 { @@ -2976,17 +2977,18 @@ static int snd_pcm_ioctl_sync_ptr_compat(struct snd_pcm_substream *substream, snd_pcm_stream_unlock_irq(substream); if (put_user(sstatus.state, &src->s.status.state) || put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) || - compat_put_timespec(&sstatus.tstamp, &src->s.status.tstamp) || + put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp_sec) || + put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp_nsec) || put_user(sstatus.suspended_state, &src->s.status.suspended_state) || - compat_put_timespec(&sstatus.audio_tstamp, - &src->s.status.audio_tstamp) || + put_user(sstatus.audio_tstamp.tv_sec, &src->s.status.audio_tstamp_sec) || + put_user(sstatus.audio_tstamp.tv_nsec, &src->s.status.audio_tstamp_nsec) || put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) || put_user(scontrol.avail_min, &src->c.control.avail_min)) return -EFAULT; return 0; } -#endif +#define __SNDRV_PCM_IOCTL_SYNC_PTR32 _IOWR('A', 0x23, struct snd_pcm_sync_ptr32) static int snd_pcm_tstamp(struct snd_pcm_substream *substream, int __user *_arg) { @@ -3156,7 +3158,9 @@ static int snd_pcm_common_ioctl(struct file *file, return -EFAULT; return 0; } - case SNDRV_PCM_IOCTL_SYNC_PTR: + case __SNDRV_PCM_IOCTL_SYNC_PTR32: + return snd_pcm_ioctl_sync_ptr_compat(substream, arg); + case __SNDRV_PCM_IOCTL_SYNC_PTR64: return snd_pcm_sync_ptr(substream, arg); #ifdef CONFIG_SND_SUPPORT_OLD_API case SNDRV_PCM_IOCTL_HW_REFINE_OLD: @@ -3494,8 +3498,6 @@ static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file static bool pcm_status_mmap_allowed(struct snd_pcm_file *pcm_file) { - if (pcm_file->no_compat_mmap) - return false; /* See pcm_control_mmap_allowed() below. * Since older alsa-lib requires both status and control mmaps to be * coupled, we have to disable the status mmap for old alsa-lib, too. @@ -3720,11 +3722,19 @@ static int snd_pcm_mmap(struct file *file, struct vm_area_struct *area) offset = area->vm_pgoff << PAGE_SHIFT; switch (offset) { - case SNDRV_PCM_MMAP_OFFSET_STATUS: + case SNDRV_PCM_MMAP_OFFSET_STATUS_OLD: + if (pcm_file->no_compat_mmap || !IS_ENABLED(CONFIG_64BIT)) + return -ENXIO; + /* fallthrough */ + case SNDRV_PCM_MMAP_OFFSET_STATUS_NEW: if (!pcm_status_mmap_allowed(pcm_file)) return -ENXIO; return snd_pcm_mmap_status(substream, file, area); - case SNDRV_PCM_MMAP_OFFSET_CONTROL: + case SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD: + if (pcm_file->no_compat_mmap || !IS_ENABLED(CONFIG_64BIT)) + return -ENXIO; + /* fallthrough */ + case SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW: if (!pcm_control_mmap_allowed(pcm_file)) return -ENXIO; return snd_pcm_mmap_control(substream, file, area); @@ -3884,9 +3894,9 @@ static unsigned long snd_pcm_get_unmapped_area(struct file *file, unsigned long offset = pgoff << PAGE_SHIFT; switch (offset) { - case SNDRV_PCM_MMAP_OFFSET_STATUS: + case SNDRV_PCM_MMAP_OFFSET_STATUS_NEW: return (unsigned long)runtime->status; - case SNDRV_PCM_MMAP_OFFSET_CONTROL: + case SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW: return (unsigned long)runtime->control; default: return (unsigned long)runtime->dma_area + offset; |