ufs: ufs_bmap_seekdata() needs mapped buffer for scan
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Authored by kib on Sun, May 17, 12:12 AM.

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mckusick
chs

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rG8ad8643a6673: ufs: ufs_bmap_seekdata() needs mapped buffer for scan

Summary

PR:     295348
Reported by:     Alastair Hogge <agh@riseup.net>
Fixes:  bab04ddf1fd4 ("ufs: support unmapped bufs for indirect blocks in bmap")

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rG FreeBSD src repository

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kib created this revision.Sun, May 17, 12:12 AM

Herald added a subscriber: imp. · View Herald TranscriptSun, May 17, 12:12 AM

kib requested review of this revision.Sun, May 17, 12:12 AM

imp added a reviewer: chs.Sun, May 17, 12:16 AM

Why does ufs_bmap_seekdata() cause a panic when it uses an unmapped buffer?

In D57036#1306961, @mckusick wrote:

Why does ufs_bmap_seekdata() cause a panic when it uses an unmapped buffer?

The function scans the indirect blocks to find holes/data if the file is large enough. Then it needs to access the indirect block content, which requires the mapping.

Unlike ufs_bmap(), which only needs to read the single value at specific index, ufs_bmap_seekdata() often needs to scan the whole buffer of the indirect block. Due to this, it does not make sense to only map single page with sf_buf.

Sorry for the delay in answering. I am in a remote area of California and the power / Internet has been out since just after I sent my question. Power outages are unfortunately routine enough for you that you can work around them, me not so much.

This revision is now accepted and ready to land.Sun, May 17, 9:56 PM

Closed by commit rG8ad8643a6673: ufs: ufs_bmap_seekdata() needs mapped buffer for scan (authored by kib). · Explain WhySun, May 17, 10:09 PM

This revision was automatically updated to reflect the committed changes.

kib added a commit: rG8ad8643a6673: ufs: ufs_bmap_seekdata() needs mapped buffer for scan.